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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /fs/eventpoll.c | |
parent | Initial commit. (diff) | |
download | linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip |
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'fs/eventpoll.c')
-rw-r--r-- | fs/eventpoll.c | 2423 |
1 files changed, 2423 insertions, 0 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c new file mode 100644 index 000000000..eccecd3fa --- /dev/null +++ b/fs/eventpoll.c @@ -0,0 +1,2423 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * fs/eventpoll.c (Efficient event retrieval implementation) + * Copyright (C) 2001,...,2009 Davide Libenzi + * + * Davide Libenzi <davidel@xmailserver.org> + */ + +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/sched/signal.h> +#include <linux/fs.h> +#include <linux/file.h> +#include <linux/signal.h> +#include <linux/errno.h> +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/poll.h> +#include <linux/string.h> +#include <linux/list.h> +#include <linux/hash.h> +#include <linux/spinlock.h> +#include <linux/syscalls.h> +#include <linux/rbtree.h> +#include <linux/wait.h> +#include <linux/eventpoll.h> +#include <linux/mount.h> +#include <linux/bitops.h> +#include <linux/mutex.h> +#include <linux/anon_inodes.h> +#include <linux/device.h> +#include <linux/uaccess.h> +#include <asm/io.h> +#include <asm/mman.h> +#include <linux/atomic.h> +#include <linux/proc_fs.h> +#include <linux/seq_file.h> +#include <linux/compat.h> +#include <linux/rculist.h> +#include <net/busy_poll.h> + +/* + * LOCKING: + * There are three level of locking required by epoll : + * + * 1) epmutex (mutex) + * 2) ep->mtx (mutex) + * 3) ep->lock (rwlock) + * + * The acquire order is the one listed above, from 1 to 3. + * We need a rwlock (ep->lock) because we manipulate objects + * from inside the poll callback, that might be triggered from + * a wake_up() that in turn might be called from IRQ context. + * So we can't sleep inside the poll callback and hence we need + * a spinlock. During the event transfer loop (from kernel to + * user space) we could end up sleeping due a copy_to_user(), so + * we need a lock that will allow us to sleep. This lock is a + * mutex (ep->mtx). It is acquired during the event transfer loop, + * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file(). + * Then we also need a global mutex to serialize eventpoll_release_file() + * and ep_free(). + * This mutex is acquired by ep_free() during the epoll file + * cleanup path and it is also acquired by eventpoll_release_file() + * if a file has been pushed inside an epoll set and it is then + * close()d without a previous call to epoll_ctl(EPOLL_CTL_DEL). + * It is also acquired when inserting an epoll fd onto another epoll + * fd. We do this so that we walk the epoll tree and ensure that this + * insertion does not create a cycle of epoll file descriptors, which + * could lead to deadlock. We need a global mutex to prevent two + * simultaneous inserts (A into B and B into A) from racing and + * constructing a cycle without either insert observing that it is + * going to. + * It is necessary to acquire multiple "ep->mtx"es at once in the + * case when one epoll fd is added to another. In this case, we + * always acquire the locks in the order of nesting (i.e. after + * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired + * before e2->mtx). Since we disallow cycles of epoll file + * descriptors, this ensures that the mutexes are well-ordered. In + * order to communicate this nesting to lockdep, when walking a tree + * of epoll file descriptors, we use the current recursion depth as + * the lockdep subkey. + * It is possible to drop the "ep->mtx" and to use the global + * mutex "epmutex" (together with "ep->lock") to have it working, + * but having "ep->mtx" will make the interface more scalable. + * Events that require holding "epmutex" are very rare, while for + * normal operations the epoll private "ep->mtx" will guarantee + * a better scalability. + */ + +/* Epoll private bits inside the event mask */ +#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET | EPOLLEXCLUSIVE) + +#define EPOLLINOUT_BITS (EPOLLIN | EPOLLOUT) + +#define EPOLLEXCLUSIVE_OK_BITS (EPOLLINOUT_BITS | EPOLLERR | EPOLLHUP | \ + EPOLLWAKEUP | EPOLLET | EPOLLEXCLUSIVE) + +/* Maximum number of nesting allowed inside epoll sets */ +#define EP_MAX_NESTS 4 + +#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) + +#define EP_UNACTIVE_PTR ((void *) -1L) + +#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry)) + +struct epoll_filefd { + struct file *file; + int fd; +} __packed; + +/* Wait structure used by the poll hooks */ +struct eppoll_entry { + /* List header used to link this structure to the "struct epitem" */ + struct eppoll_entry *next; + + /* The "base" pointer is set to the container "struct epitem" */ + struct epitem *base; + + /* + * Wait queue item that will be linked to the target file wait + * queue head. + */ + wait_queue_entry_t wait; + + /* The wait queue head that linked the "wait" wait queue item */ + wait_queue_head_t *whead; +}; + +/* + * Each file descriptor added to the eventpoll interface will + * have an entry of this type linked to the "rbr" RB tree. + * Avoid increasing the size of this struct, there can be many thousands + * of these on a server and we do not want this to take another cache line. + */ +struct epitem { + union { + /* RB tree node links this structure to the eventpoll RB tree */ + struct rb_node rbn; + /* Used to free the struct epitem */ + struct rcu_head rcu; + }; + + /* List header used to link this structure to the eventpoll ready list */ + struct list_head rdllink; + + /* + * Works together "struct eventpoll"->ovflist in keeping the + * single linked chain of items. + */ + struct epitem *next; + + /* The file descriptor information this item refers to */ + struct epoll_filefd ffd; + + /* List containing poll wait queues */ + struct eppoll_entry *pwqlist; + + /* The "container" of this item */ + struct eventpoll *ep; + + /* List header used to link this item to the "struct file" items list */ + struct hlist_node fllink; + + /* wakeup_source used when EPOLLWAKEUP is set */ + struct wakeup_source __rcu *ws; + + /* The structure that describe the interested events and the source fd */ + struct epoll_event event; +}; + +/* + * This structure is stored inside the "private_data" member of the file + * structure and represents the main data structure for the eventpoll + * interface. + */ +struct eventpoll { + /* + * This mutex is used to ensure that files are not removed + * while epoll is using them. This is held during the event + * collection loop, the file cleanup path, the epoll file exit + * code and the ctl operations. + */ + struct mutex mtx; + + /* Wait queue used by sys_epoll_wait() */ + wait_queue_head_t wq; + + /* Wait queue used by file->poll() */ + wait_queue_head_t poll_wait; + + /* List of ready file descriptors */ + struct list_head rdllist; + + /* Lock which protects rdllist and ovflist */ + rwlock_t lock; + + /* RB tree root used to store monitored fd structs */ + struct rb_root_cached rbr; + + /* + * This is a single linked list that chains all the "struct epitem" that + * happened while transferring ready events to userspace w/out + * holding ->lock. + */ + struct epitem *ovflist; + + /* wakeup_source used when ep_scan_ready_list is running */ + struct wakeup_source *ws; + + /* The user that created the eventpoll descriptor */ + struct user_struct *user; + + struct file *file; + + /* used to optimize loop detection check */ + u64 gen; + struct hlist_head refs; + +#ifdef CONFIG_NET_RX_BUSY_POLL + /* used to track busy poll napi_id */ + unsigned int napi_id; +#endif + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + /* tracks wakeup nests for lockdep validation */ + u8 nests; +#endif +}; + +/* Wrapper struct used by poll queueing */ +struct ep_pqueue { + poll_table pt; + struct epitem *epi; +}; + +/* + * Configuration options available inside /proc/sys/fs/epoll/ + */ +/* Maximum number of epoll watched descriptors, per user */ +static long max_user_watches __read_mostly; + +/* + * This mutex is used to serialize ep_free() and eventpoll_release_file(). + */ +static DEFINE_MUTEX(epmutex); + +static u64 loop_check_gen = 0; + +/* Used to check for epoll file descriptor inclusion loops */ +static struct eventpoll *inserting_into; + +/* Slab cache used to allocate "struct epitem" */ +static struct kmem_cache *epi_cache __read_mostly; + +/* Slab cache used to allocate "struct eppoll_entry" */ +static struct kmem_cache *pwq_cache __read_mostly; + +/* + * List of files with newly added links, where we may need to limit the number + * of emanating paths. Protected by the epmutex. + */ +struct epitems_head { + struct hlist_head epitems; + struct epitems_head *next; +}; +static struct epitems_head *tfile_check_list = EP_UNACTIVE_PTR; + +static struct kmem_cache *ephead_cache __read_mostly; + +static inline void free_ephead(struct epitems_head *head) +{ + if (head) + kmem_cache_free(ephead_cache, head); +} + +static void list_file(struct file *file) +{ + struct epitems_head *head; + + head = container_of(file->f_ep, struct epitems_head, epitems); + if (!head->next) { + head->next = tfile_check_list; + tfile_check_list = head; + } +} + +static void unlist_file(struct epitems_head *head) +{ + struct epitems_head *to_free = head; + struct hlist_node *p = rcu_dereference(hlist_first_rcu(&head->epitems)); + if (p) { + struct epitem *epi= container_of(p, struct epitem, fllink); + spin_lock(&epi->ffd.file->f_lock); + if (!hlist_empty(&head->epitems)) + to_free = NULL; + head->next = NULL; + spin_unlock(&epi->ffd.file->f_lock); + } + free_ephead(to_free); +} + +#ifdef CONFIG_SYSCTL + +#include <linux/sysctl.h> + +static long long_zero; +static long long_max = LONG_MAX; + +static struct ctl_table epoll_table[] = { + { + .procname = "max_user_watches", + .data = &max_user_watches, + .maxlen = sizeof(max_user_watches), + .mode = 0644, + .proc_handler = proc_doulongvec_minmax, + .extra1 = &long_zero, + .extra2 = &long_max, + }, + { } +}; + +static void __init epoll_sysctls_init(void) +{ + register_sysctl("fs/epoll", epoll_table); +} +#else +#define epoll_sysctls_init() do { } while (0) +#endif /* CONFIG_SYSCTL */ + +static const struct file_operations eventpoll_fops; + +static inline int is_file_epoll(struct file *f) +{ + return f->f_op == &eventpoll_fops; +} + +/* Setup the structure that is used as key for the RB tree */ +static inline void ep_set_ffd(struct epoll_filefd *ffd, + struct file *file, int fd) +{ + ffd->file = file; + ffd->fd = fd; +} + +/* Compare RB tree keys */ +static inline int ep_cmp_ffd(struct epoll_filefd *p1, + struct epoll_filefd *p2) +{ + return (p1->file > p2->file ? +1: + (p1->file < p2->file ? -1 : p1->fd - p2->fd)); +} + +/* Tells us if the item is currently linked */ +static inline int ep_is_linked(struct epitem *epi) +{ + return !list_empty(&epi->rdllink); +} + +static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_entry_t *p) +{ + return container_of(p, struct eppoll_entry, wait); +} + +/* Get the "struct epitem" from a wait queue pointer */ +static inline struct epitem *ep_item_from_wait(wait_queue_entry_t *p) +{ + return container_of(p, struct eppoll_entry, wait)->base; +} + +/** + * ep_events_available - Checks if ready events might be available. + * + * @ep: Pointer to the eventpoll context. + * + * Return: a value different than %zero if ready events are available, + * or %zero otherwise. + */ +static inline int ep_events_available(struct eventpoll *ep) +{ + return !list_empty_careful(&ep->rdllist) || + READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR; +} + +#ifdef CONFIG_NET_RX_BUSY_POLL +static bool ep_busy_loop_end(void *p, unsigned long start_time) +{ + struct eventpoll *ep = p; + + return ep_events_available(ep) || busy_loop_timeout(start_time); +} + +/* + * Busy poll if globally on and supporting sockets found && no events, + * busy loop will return if need_resched or ep_events_available. + * + * we must do our busy polling with irqs enabled + */ +static bool ep_busy_loop(struct eventpoll *ep, int nonblock) +{ + unsigned int napi_id = READ_ONCE(ep->napi_id); + + if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) { + napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false, + BUSY_POLL_BUDGET); + if (ep_events_available(ep)) + return true; + /* + * Busy poll timed out. Drop NAPI ID for now, we can add + * it back in when we have moved a socket with a valid NAPI + * ID onto the ready list. + */ + ep->napi_id = 0; + return false; + } + return false; +} + +/* + * Set epoll busy poll NAPI ID from sk. + */ +static inline void ep_set_busy_poll_napi_id(struct epitem *epi) +{ + struct eventpoll *ep; + unsigned int napi_id; + struct socket *sock; + struct sock *sk; + + if (!net_busy_loop_on()) + return; + + sock = sock_from_file(epi->ffd.file); + if (!sock) + return; + + sk = sock->sk; + if (!sk) + return; + + napi_id = READ_ONCE(sk->sk_napi_id); + ep = epi->ep; + + /* Non-NAPI IDs can be rejected + * or + * Nothing to do if we already have this ID + */ + if (napi_id < MIN_NAPI_ID || napi_id == ep->napi_id) + return; + + /* record NAPI ID for use in next busy poll */ + ep->napi_id = napi_id; +} + +#else + +static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock) +{ + return false; +} + +static inline void ep_set_busy_poll_napi_id(struct epitem *epi) +{ +} + +#endif /* CONFIG_NET_RX_BUSY_POLL */ + +/* + * As described in commit 0ccf831cb lockdep: annotate epoll + * the use of wait queues used by epoll is done in a very controlled + * manner. Wake ups can nest inside each other, but are never done + * with the same locking. For example: + * + * dfd = socket(...); + * efd1 = epoll_create(); + * efd2 = epoll_create(); + * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); + * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); + * + * When a packet arrives to the device underneath "dfd", the net code will + * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a + * callback wakeup entry on that queue, and the wake_up() performed by the + * "dfd" net code will end up in ep_poll_callback(). At this point epoll + * (efd1) notices that it may have some event ready, so it needs to wake up + * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() + * that ends up in another wake_up(), after having checked about the + * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to + * avoid stack blasting. + * + * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle + * this special case of epoll. + */ +#ifdef CONFIG_DEBUG_LOCK_ALLOC + +static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, + unsigned pollflags) +{ + struct eventpoll *ep_src; + unsigned long flags; + u8 nests = 0; + + /* + * To set the subclass or nesting level for spin_lock_irqsave_nested() + * it might be natural to create a per-cpu nest count. However, since + * we can recurse on ep->poll_wait.lock, and a non-raw spinlock can + * schedule() in the -rt kernel, the per-cpu variable are no longer + * protected. Thus, we are introducing a per eventpoll nest field. + * If we are not being call from ep_poll_callback(), epi is NULL and + * we are at the first level of nesting, 0. Otherwise, we are being + * called from ep_poll_callback() and if a previous wakeup source is + * not an epoll file itself, we are at depth 1 since the wakeup source + * is depth 0. If the wakeup source is a previous epoll file in the + * wakeup chain then we use its nests value and record ours as + * nests + 1. The previous epoll file nests value is stable since its + * already holding its own poll_wait.lock. + */ + if (epi) { + if ((is_file_epoll(epi->ffd.file))) { + ep_src = epi->ffd.file->private_data; + nests = ep_src->nests; + } else { + nests = 1; + } + } + spin_lock_irqsave_nested(&ep->poll_wait.lock, flags, nests); + ep->nests = nests + 1; + wake_up_locked_poll(&ep->poll_wait, EPOLLIN | pollflags); + ep->nests = 0; + spin_unlock_irqrestore(&ep->poll_wait.lock, flags); +} + +#else + +static void ep_poll_safewake(struct eventpoll *ep, struct epitem *epi, + unsigned pollflags) +{ + wake_up_poll(&ep->poll_wait, EPOLLIN | pollflags); +} + +#endif + +static void ep_remove_wait_queue(struct eppoll_entry *pwq) +{ + wait_queue_head_t *whead; + + rcu_read_lock(); + /* + * If it is cleared by POLLFREE, it should be rcu-safe. + * If we read NULL we need a barrier paired with + * smp_store_release() in ep_poll_callback(), otherwise + * we rely on whead->lock. + */ + whead = smp_load_acquire(&pwq->whead); + if (whead) + remove_wait_queue(whead, &pwq->wait); + rcu_read_unlock(); +} + +/* + * This function unregisters poll callbacks from the associated file + * descriptor. Must be called with "mtx" held (or "epmutex" if called from + * ep_free). + */ +static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) +{ + struct eppoll_entry **p = &epi->pwqlist; + struct eppoll_entry *pwq; + + while ((pwq = *p) != NULL) { + *p = pwq->next; + ep_remove_wait_queue(pwq); + kmem_cache_free(pwq_cache, pwq); + } +} + +/* call only when ep->mtx is held */ +static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi) +{ + return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx)); +} + +/* call only when ep->mtx is held */ +static inline void ep_pm_stay_awake(struct epitem *epi) +{ + struct wakeup_source *ws = ep_wakeup_source(epi); + + if (ws) + __pm_stay_awake(ws); +} + +static inline bool ep_has_wakeup_source(struct epitem *epi) +{ + return rcu_access_pointer(epi->ws) ? true : false; +} + +/* call when ep->mtx cannot be held (ep_poll_callback) */ +static inline void ep_pm_stay_awake_rcu(struct epitem *epi) +{ + struct wakeup_source *ws; + + rcu_read_lock(); + ws = rcu_dereference(epi->ws); + if (ws) + __pm_stay_awake(ws); + rcu_read_unlock(); +} + + +/* + * ep->mutex needs to be held because we could be hit by + * eventpoll_release_file() and epoll_ctl(). + */ +static void ep_start_scan(struct eventpoll *ep, struct list_head *txlist) +{ + /* + * Steal the ready list, and re-init the original one to the + * empty list. Also, set ep->ovflist to NULL so that events + * happening while looping w/out locks, are not lost. We cannot + * have the poll callback to queue directly on ep->rdllist, + * because we want the "sproc" callback to be able to do it + * in a lockless way. + */ + lockdep_assert_irqs_enabled(); + write_lock_irq(&ep->lock); + list_splice_init(&ep->rdllist, txlist); + WRITE_ONCE(ep->ovflist, NULL); + write_unlock_irq(&ep->lock); +} + +static void ep_done_scan(struct eventpoll *ep, + struct list_head *txlist) +{ + struct epitem *epi, *nepi; + + write_lock_irq(&ep->lock); + /* + * During the time we spent inside the "sproc" callback, some + * other events might have been queued by the poll callback. + * We re-insert them inside the main ready-list here. + */ + for (nepi = READ_ONCE(ep->ovflist); (epi = nepi) != NULL; + nepi = epi->next, epi->next = EP_UNACTIVE_PTR) { + /* + * We need to check if the item is already in the list. + * During the "sproc" callback execution time, items are + * queued into ->ovflist but the "txlist" might already + * contain them, and the list_splice() below takes care of them. + */ + if (!ep_is_linked(epi)) { + /* + * ->ovflist is LIFO, so we have to reverse it in order + * to keep in FIFO. + */ + list_add(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + } + } + /* + * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after + * releasing the lock, events will be queued in the normal way inside + * ep->rdllist. + */ + WRITE_ONCE(ep->ovflist, EP_UNACTIVE_PTR); + + /* + * Quickly re-inject items left on "txlist". + */ + list_splice(txlist, &ep->rdllist); + __pm_relax(ep->ws); + + if (!list_empty(&ep->rdllist)) { + if (waitqueue_active(&ep->wq)) + wake_up(&ep->wq); + } + + write_unlock_irq(&ep->lock); +} + +static void epi_rcu_free(struct rcu_head *head) +{ + struct epitem *epi = container_of(head, struct epitem, rcu); + kmem_cache_free(epi_cache, epi); +} + +/* + * Removes a "struct epitem" from the eventpoll RB tree and deallocates + * all the associated resources. Must be called with "mtx" held. + */ +static int ep_remove(struct eventpoll *ep, struct epitem *epi) +{ + struct file *file = epi->ffd.file; + struct epitems_head *to_free; + struct hlist_head *head; + + lockdep_assert_irqs_enabled(); + + /* + * Removes poll wait queue hooks. + */ + ep_unregister_pollwait(ep, epi); + + /* Remove the current item from the list of epoll hooks */ + spin_lock(&file->f_lock); + to_free = NULL; + head = file->f_ep; + if (head->first == &epi->fllink && !epi->fllink.next) { + file->f_ep = NULL; + if (!is_file_epoll(file)) { + struct epitems_head *v; + v = container_of(head, struct epitems_head, epitems); + if (!smp_load_acquire(&v->next)) + to_free = v; + } + } + hlist_del_rcu(&epi->fllink); + spin_unlock(&file->f_lock); + free_ephead(to_free); + + rb_erase_cached(&epi->rbn, &ep->rbr); + + write_lock_irq(&ep->lock); + if (ep_is_linked(epi)) + list_del_init(&epi->rdllink); + write_unlock_irq(&ep->lock); + + wakeup_source_unregister(ep_wakeup_source(epi)); + /* + * At this point it is safe to free the eventpoll item. Use the union + * field epi->rcu, since we are trying to minimize the size of + * 'struct epitem'. The 'rbn' field is no longer in use. Protected by + * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make + * use of the rbn field. + */ + call_rcu(&epi->rcu, epi_rcu_free); + + percpu_counter_dec(&ep->user->epoll_watches); + + return 0; +} + +static void ep_free(struct eventpoll *ep) +{ + struct rb_node *rbp; + struct epitem *epi; + + /* We need to release all tasks waiting for these file */ + if (waitqueue_active(&ep->poll_wait)) + ep_poll_safewake(ep, NULL, 0); + + /* + * We need to lock this because we could be hit by + * eventpoll_release_file() while we're freeing the "struct eventpoll". + * We do not need to hold "ep->mtx" here because the epoll file + * is on the way to be removed and no one has references to it + * anymore. The only hit might come from eventpoll_release_file() but + * holding "epmutex" is sufficient here. + */ + mutex_lock(&epmutex); + + /* + * Walks through the whole tree by unregistering poll callbacks. + */ + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + + ep_unregister_pollwait(ep, epi); + cond_resched(); + } + + /* + * Walks through the whole tree by freeing each "struct epitem". At this + * point we are sure no poll callbacks will be lingering around, and also by + * holding "epmutex" we can be sure that no file cleanup code will hit + * us during this operation. So we can avoid the lock on "ep->lock". + * We do not need to lock ep->mtx, either, we only do it to prevent + * a lockdep warning. + */ + mutex_lock(&ep->mtx); + while ((rbp = rb_first_cached(&ep->rbr)) != NULL) { + epi = rb_entry(rbp, struct epitem, rbn); + ep_remove(ep, epi); + cond_resched(); + } + mutex_unlock(&ep->mtx); + + mutex_unlock(&epmutex); + mutex_destroy(&ep->mtx); + free_uid(ep->user); + wakeup_source_unregister(ep->ws); + kfree(ep); +} + +static int ep_eventpoll_release(struct inode *inode, struct file *file) +{ + struct eventpoll *ep = file->private_data; + + if (ep) + ep_free(ep); + + return 0; +} + +static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, int depth); + +static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int depth) +{ + struct eventpoll *ep = file->private_data; + LIST_HEAD(txlist); + struct epitem *epi, *tmp; + poll_table pt; + __poll_t res = 0; + + init_poll_funcptr(&pt, NULL); + + /* Insert inside our poll wait queue */ + poll_wait(file, &ep->poll_wait, wait); + + /* + * Proceed to find out if wanted events are really available inside + * the ready list. + */ + mutex_lock_nested(&ep->mtx, depth); + ep_start_scan(ep, &txlist); + list_for_each_entry_safe(epi, tmp, &txlist, rdllink) { + if (ep_item_poll(epi, &pt, depth + 1)) { + res = EPOLLIN | EPOLLRDNORM; + break; + } else { + /* + * Item has been dropped into the ready list by the poll + * callback, but it's not actually ready, as far as + * caller requested events goes. We can remove it here. + */ + __pm_relax(ep_wakeup_source(epi)); + list_del_init(&epi->rdllink); + } + } + ep_done_scan(ep, &txlist); + mutex_unlock(&ep->mtx); + return res; +} + +/* + * Differs from ep_eventpoll_poll() in that internal callers already have + * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested() + * is correctly annotated. + */ +static __poll_t ep_item_poll(const struct epitem *epi, poll_table *pt, + int depth) +{ + struct file *file = epi->ffd.file; + __poll_t res; + + pt->_key = epi->event.events; + if (!is_file_epoll(file)) + res = vfs_poll(file, pt); + else + res = __ep_eventpoll_poll(file, pt, depth); + return res & epi->event.events; +} + +static __poll_t ep_eventpoll_poll(struct file *file, poll_table *wait) +{ + return __ep_eventpoll_poll(file, wait, 0); +} + +#ifdef CONFIG_PROC_FS +static void ep_show_fdinfo(struct seq_file *m, struct file *f) +{ + struct eventpoll *ep = f->private_data; + struct rb_node *rbp; + + mutex_lock(&ep->mtx); + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + struct epitem *epi = rb_entry(rbp, struct epitem, rbn); + struct inode *inode = file_inode(epi->ffd.file); + + seq_printf(m, "tfd: %8d events: %8x data: %16llx " + " pos:%lli ino:%lx sdev:%x\n", + epi->ffd.fd, epi->event.events, + (long long)epi->event.data, + (long long)epi->ffd.file->f_pos, + inode->i_ino, inode->i_sb->s_dev); + if (seq_has_overflowed(m)) + break; + } + mutex_unlock(&ep->mtx); +} +#endif + +/* File callbacks that implement the eventpoll file behaviour */ +static const struct file_operations eventpoll_fops = { +#ifdef CONFIG_PROC_FS + .show_fdinfo = ep_show_fdinfo, +#endif + .release = ep_eventpoll_release, + .poll = ep_eventpoll_poll, + .llseek = noop_llseek, +}; + +/* + * This is called from eventpoll_release() to unlink files from the eventpoll + * interface. We need to have this facility to cleanup correctly files that are + * closed without being removed from the eventpoll interface. + */ +void eventpoll_release_file(struct file *file) +{ + struct eventpoll *ep; + struct epitem *epi; + struct hlist_node *next; + + /* + * We don't want to get "file->f_lock" because it is not + * necessary. It is not necessary because we're in the "struct file" + * cleanup path, and this means that no one is using this file anymore. + * So, for example, epoll_ctl() cannot hit here since if we reach this + * point, the file counter already went to zero and fget() would fail. + * The only hit might come from ep_free() but by holding the mutex + * will correctly serialize the operation. We do need to acquire + * "ep->mtx" after "epmutex" because ep_remove() requires it when called + * from anywhere but ep_free(). + * + * Besides, ep_remove() acquires the lock, so we can't hold it here. + */ + mutex_lock(&epmutex); + if (unlikely(!file->f_ep)) { + mutex_unlock(&epmutex); + return; + } + hlist_for_each_entry_safe(epi, next, file->f_ep, fllink) { + ep = epi->ep; + mutex_lock_nested(&ep->mtx, 0); + ep_remove(ep, epi); + mutex_unlock(&ep->mtx); + } + mutex_unlock(&epmutex); +} + +static int ep_alloc(struct eventpoll **pep) +{ + int error; + struct user_struct *user; + struct eventpoll *ep; + + user = get_current_user(); + error = -ENOMEM; + ep = kzalloc(sizeof(*ep), GFP_KERNEL); + if (unlikely(!ep)) + goto free_uid; + + mutex_init(&ep->mtx); + rwlock_init(&ep->lock); + init_waitqueue_head(&ep->wq); + init_waitqueue_head(&ep->poll_wait); + INIT_LIST_HEAD(&ep->rdllist); + ep->rbr = RB_ROOT_CACHED; + ep->ovflist = EP_UNACTIVE_PTR; + ep->user = user; + + *pep = ep; + + return 0; + +free_uid: + free_uid(user); + return error; +} + +/* + * Search the file inside the eventpoll tree. The RB tree operations + * are protected by the "mtx" mutex, and ep_find() must be called with + * "mtx" held. + */ +static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) +{ + int kcmp; + struct rb_node *rbp; + struct epitem *epi, *epir = NULL; + struct epoll_filefd ffd; + + ep_set_ffd(&ffd, file, fd); + for (rbp = ep->rbr.rb_root.rb_node; rbp; ) { + epi = rb_entry(rbp, struct epitem, rbn); + kcmp = ep_cmp_ffd(&ffd, &epi->ffd); + if (kcmp > 0) + rbp = rbp->rb_right; + else if (kcmp < 0) + rbp = rbp->rb_left; + else { + epir = epi; + break; + } + } + + return epir; +} + +#ifdef CONFIG_KCMP +static struct epitem *ep_find_tfd(struct eventpoll *ep, int tfd, unsigned long toff) +{ + struct rb_node *rbp; + struct epitem *epi; + + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + if (epi->ffd.fd == tfd) { + if (toff == 0) + return epi; + else + toff--; + } + cond_resched(); + } + + return NULL; +} + +struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, + unsigned long toff) +{ + struct file *file_raw; + struct eventpoll *ep; + struct epitem *epi; + + if (!is_file_epoll(file)) + return ERR_PTR(-EINVAL); + + ep = file->private_data; + + mutex_lock(&ep->mtx); + epi = ep_find_tfd(ep, tfd, toff); + if (epi) + file_raw = epi->ffd.file; + else + file_raw = ERR_PTR(-ENOENT); + mutex_unlock(&ep->mtx); + + return file_raw; +} +#endif /* CONFIG_KCMP */ + +/* + * Adds a new entry to the tail of the list in a lockless way, i.e. + * multiple CPUs are allowed to call this function concurrently. + * + * Beware: it is necessary to prevent any other modifications of the + * existing list until all changes are completed, in other words + * concurrent list_add_tail_lockless() calls should be protected + * with a read lock, where write lock acts as a barrier which + * makes sure all list_add_tail_lockless() calls are fully + * completed. + * + * Also an element can be locklessly added to the list only in one + * direction i.e. either to the tail or to the head, otherwise + * concurrent access will corrupt the list. + * + * Return: %false if element has been already added to the list, %true + * otherwise. + */ +static inline bool list_add_tail_lockless(struct list_head *new, + struct list_head *head) +{ + struct list_head *prev; + + /* + * This is simple 'new->next = head' operation, but cmpxchg() + * is used in order to detect that same element has been just + * added to the list from another CPU: the winner observes + * new->next == new. + */ + if (!try_cmpxchg(&new->next, &new, head)) + return false; + + /* + * Initially ->next of a new element must be updated with the head + * (we are inserting to the tail) and only then pointers are atomically + * exchanged. XCHG guarantees memory ordering, thus ->next should be + * updated before pointers are actually swapped and pointers are + * swapped before prev->next is updated. + */ + + prev = xchg(&head->prev, new); + + /* + * It is safe to modify prev->next and new->prev, because a new element + * is added only to the tail and new->next is updated before XCHG. + */ + + prev->next = new; + new->prev = prev; + + return true; +} + +/* + * Chains a new epi entry to the tail of the ep->ovflist in a lockless way, + * i.e. multiple CPUs are allowed to call this function concurrently. + * + * Return: %false if epi element has been already chained, %true otherwise. + */ +static inline bool chain_epi_lockless(struct epitem *epi) +{ + struct eventpoll *ep = epi->ep; + + /* Fast preliminary check */ + if (epi->next != EP_UNACTIVE_PTR) + return false; + + /* Check that the same epi has not been just chained from another CPU */ + if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR) + return false; + + /* Atomically exchange tail */ + epi->next = xchg(&ep->ovflist, epi); + + return true; +} + +/* + * This is the callback that is passed to the wait queue wakeup + * mechanism. It is called by the stored file descriptors when they + * have events to report. + * + * This callback takes a read lock in order not to contend with concurrent + * events from another file descriptor, thus all modifications to ->rdllist + * or ->ovflist are lockless. Read lock is paired with the write lock from + * ep_scan_ready_list(), which stops all list modifications and guarantees + * that lists state is seen correctly. + * + * Another thing worth to mention is that ep_poll_callback() can be called + * concurrently for the same @epi from different CPUs if poll table was inited + * with several wait queues entries. Plural wakeup from different CPUs of a + * single wait queue is serialized by wq.lock, but the case when multiple wait + * queues are used should be detected accordingly. This is detected using + * cmpxchg() operation. + */ +static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key) +{ + int pwake = 0; + struct epitem *epi = ep_item_from_wait(wait); + struct eventpoll *ep = epi->ep; + __poll_t pollflags = key_to_poll(key); + unsigned long flags; + int ewake = 0; + + read_lock_irqsave(&ep->lock, flags); + + ep_set_busy_poll_napi_id(epi); + + /* + * If the event mask does not contain any poll(2) event, we consider the + * descriptor to be disabled. This condition is likely the effect of the + * EPOLLONESHOT bit that disables the descriptor when an event is received, + * until the next EPOLL_CTL_MOD will be issued. + */ + if (!(epi->event.events & ~EP_PRIVATE_BITS)) + goto out_unlock; + + /* + * Check the events coming with the callback. At this stage, not + * every device reports the events in the "key" parameter of the + * callback. We need to be able to handle both cases here, hence the + * test for "key" != NULL before the event match test. + */ + if (pollflags && !(pollflags & epi->event.events)) + goto out_unlock; + + /* + * If we are transferring events to userspace, we can hold no locks + * (because we're accessing user memory, and because of linux f_op->poll() + * semantics). All the events that happen during that period of time are + * chained in ep->ovflist and requeued later on. + */ + if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) { + if (chain_epi_lockless(epi)) + ep_pm_stay_awake_rcu(epi); + } else if (!ep_is_linked(epi)) { + /* In the usual case, add event to ready list. */ + if (list_add_tail_lockless(&epi->rdllink, &ep->rdllist)) + ep_pm_stay_awake_rcu(epi); + } + + /* + * Wake up ( if active ) both the eventpoll wait list and the ->poll() + * wait list. + */ + if (waitqueue_active(&ep->wq)) { + if ((epi->event.events & EPOLLEXCLUSIVE) && + !(pollflags & POLLFREE)) { + switch (pollflags & EPOLLINOUT_BITS) { + case EPOLLIN: + if (epi->event.events & EPOLLIN) + ewake = 1; + break; + case EPOLLOUT: + if (epi->event.events & EPOLLOUT) + ewake = 1; + break; + case 0: + ewake = 1; + break; + } + } + wake_up(&ep->wq); + } + if (waitqueue_active(&ep->poll_wait)) + pwake++; + +out_unlock: + read_unlock_irqrestore(&ep->lock, flags); + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(ep, epi, pollflags & EPOLL_URING_WAKE); + + if (!(epi->event.events & EPOLLEXCLUSIVE)) + ewake = 1; + + if (pollflags & POLLFREE) { + /* + * If we race with ep_remove_wait_queue() it can miss + * ->whead = NULL and do another remove_wait_queue() after + * us, so we can't use __remove_wait_queue(). + */ + list_del_init(&wait->entry); + /* + * ->whead != NULL protects us from the race with ep_free() + * or ep_remove(), ep_remove_wait_queue() takes whead->lock + * held by the caller. Once we nullify it, nothing protects + * ep/epi or even wait. + */ + smp_store_release(&ep_pwq_from_wait(wait)->whead, NULL); + } + + return ewake; +} + +/* + * This is the callback that is used to add our wait queue to the + * target file wakeup lists. + */ +static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, + poll_table *pt) +{ + struct ep_pqueue *epq = container_of(pt, struct ep_pqueue, pt); + struct epitem *epi = epq->epi; + struct eppoll_entry *pwq; + + if (unlikely(!epi)) // an earlier allocation has failed + return; + + pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL); + if (unlikely(!pwq)) { + epq->epi = NULL; + return; + } + + init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); + pwq->whead = whead; + pwq->base = epi; + if (epi->event.events & EPOLLEXCLUSIVE) + add_wait_queue_exclusive(whead, &pwq->wait); + else + add_wait_queue(whead, &pwq->wait); + pwq->next = epi->pwqlist; + epi->pwqlist = pwq; +} + +static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi) +{ + int kcmp; + struct rb_node **p = &ep->rbr.rb_root.rb_node, *parent = NULL; + struct epitem *epic; + bool leftmost = true; + + while (*p) { + parent = *p; + epic = rb_entry(parent, struct epitem, rbn); + kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); + if (kcmp > 0) { + p = &parent->rb_right; + leftmost = false; + } else + p = &parent->rb_left; + } + rb_link_node(&epi->rbn, parent, p); + rb_insert_color_cached(&epi->rbn, &ep->rbr, leftmost); +} + + + +#define PATH_ARR_SIZE 5 +/* + * These are the number paths of length 1 to 5, that we are allowing to emanate + * from a single file of interest. For example, we allow 1000 paths of length + * 1, to emanate from each file of interest. This essentially represents the + * potential wakeup paths, which need to be limited in order to avoid massive + * uncontrolled wakeup storms. The common use case should be a single ep which + * is connected to n file sources. In this case each file source has 1 path + * of length 1. Thus, the numbers below should be more than sufficient. These + * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify + * and delete can't add additional paths. Protected by the epmutex. + */ +static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 }; +static int path_count[PATH_ARR_SIZE]; + +static int path_count_inc(int nests) +{ + /* Allow an arbitrary number of depth 1 paths */ + if (nests == 0) + return 0; + + if (++path_count[nests] > path_limits[nests]) + return -1; + return 0; +} + +static void path_count_init(void) +{ + int i; + + for (i = 0; i < PATH_ARR_SIZE; i++) + path_count[i] = 0; +} + +static int reverse_path_check_proc(struct hlist_head *refs, int depth) +{ + int error = 0; + struct epitem *epi; + + if (depth > EP_MAX_NESTS) /* too deep nesting */ + return -1; + + /* CTL_DEL can remove links here, but that can't increase our count */ + hlist_for_each_entry_rcu(epi, refs, fllink) { + struct hlist_head *refs = &epi->ep->refs; + if (hlist_empty(refs)) + error = path_count_inc(depth); + else + error = reverse_path_check_proc(refs, depth + 1); + if (error != 0) + break; + } + return error; +} + +/** + * reverse_path_check - The tfile_check_list is list of epitem_head, which have + * links that are proposed to be newly added. We need to + * make sure that those added links don't add too many + * paths such that we will spend all our time waking up + * eventpoll objects. + * + * Return: %zero if the proposed links don't create too many paths, + * %-1 otherwise. + */ +static int reverse_path_check(void) +{ + struct epitems_head *p; + + for (p = tfile_check_list; p != EP_UNACTIVE_PTR; p = p->next) { + int error; + path_count_init(); + rcu_read_lock(); + error = reverse_path_check_proc(&p->epitems, 0); + rcu_read_unlock(); + if (error) + return error; + } + return 0; +} + +static int ep_create_wakeup_source(struct epitem *epi) +{ + struct name_snapshot n; + struct wakeup_source *ws; + + if (!epi->ep->ws) { + epi->ep->ws = wakeup_source_register(NULL, "eventpoll"); + if (!epi->ep->ws) + return -ENOMEM; + } + + take_dentry_name_snapshot(&n, epi->ffd.file->f_path.dentry); + ws = wakeup_source_register(NULL, n.name.name); + release_dentry_name_snapshot(&n); + + if (!ws) + return -ENOMEM; + rcu_assign_pointer(epi->ws, ws); + + return 0; +} + +/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */ +static noinline void ep_destroy_wakeup_source(struct epitem *epi) +{ + struct wakeup_source *ws = ep_wakeup_source(epi); + + RCU_INIT_POINTER(epi->ws, NULL); + + /* + * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is + * used internally by wakeup_source_remove, too (called by + * wakeup_source_unregister), so we cannot use call_rcu + */ + synchronize_rcu(); + wakeup_source_unregister(ws); +} + +static int attach_epitem(struct file *file, struct epitem *epi) +{ + struct epitems_head *to_free = NULL; + struct hlist_head *head = NULL; + struct eventpoll *ep = NULL; + + if (is_file_epoll(file)) + ep = file->private_data; + + if (ep) { + head = &ep->refs; + } else if (!READ_ONCE(file->f_ep)) { +allocate: + to_free = kmem_cache_zalloc(ephead_cache, GFP_KERNEL); + if (!to_free) + return -ENOMEM; + head = &to_free->epitems; + } + spin_lock(&file->f_lock); + if (!file->f_ep) { + if (unlikely(!head)) { + spin_unlock(&file->f_lock); + goto allocate; + } + file->f_ep = head; + to_free = NULL; + } + hlist_add_head_rcu(&epi->fllink, file->f_ep); + spin_unlock(&file->f_lock); + free_ephead(to_free); + return 0; +} + +/* + * Must be called with "mtx" held. + */ +static int ep_insert(struct eventpoll *ep, const struct epoll_event *event, + struct file *tfile, int fd, int full_check) +{ + int error, pwake = 0; + __poll_t revents; + struct epitem *epi; + struct ep_pqueue epq; + struct eventpoll *tep = NULL; + + if (is_file_epoll(tfile)) + tep = tfile->private_data; + + lockdep_assert_irqs_enabled(); + + if (unlikely(percpu_counter_compare(&ep->user->epoll_watches, + max_user_watches) >= 0)) + return -ENOSPC; + percpu_counter_inc(&ep->user->epoll_watches); + + if (!(epi = kmem_cache_zalloc(epi_cache, GFP_KERNEL))) { + percpu_counter_dec(&ep->user->epoll_watches); + return -ENOMEM; + } + + /* Item initialization follow here ... */ + INIT_LIST_HEAD(&epi->rdllink); + epi->ep = ep; + ep_set_ffd(&epi->ffd, tfile, fd); + epi->event = *event; + epi->next = EP_UNACTIVE_PTR; + + if (tep) + mutex_lock_nested(&tep->mtx, 1); + /* Add the current item to the list of active epoll hook for this file */ + if (unlikely(attach_epitem(tfile, epi) < 0)) { + if (tep) + mutex_unlock(&tep->mtx); + kmem_cache_free(epi_cache, epi); + percpu_counter_dec(&ep->user->epoll_watches); + return -ENOMEM; + } + + if (full_check && !tep) + list_file(tfile); + + /* + * Add the current item to the RB tree. All RB tree operations are + * protected by "mtx", and ep_insert() is called with "mtx" held. + */ + ep_rbtree_insert(ep, epi); + if (tep) + mutex_unlock(&tep->mtx); + + /* now check if we've created too many backpaths */ + if (unlikely(full_check && reverse_path_check())) { + ep_remove(ep, epi); + return -EINVAL; + } + + if (epi->event.events & EPOLLWAKEUP) { + error = ep_create_wakeup_source(epi); + if (error) { + ep_remove(ep, epi); + return error; + } + } + + /* Initialize the poll table using the queue callback */ + epq.epi = epi; + init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); + + /* + * Attach the item to the poll hooks and get current event bits. + * We can safely use the file* here because its usage count has + * been increased by the caller of this function. Note that after + * this operation completes, the poll callback can start hitting + * the new item. + */ + revents = ep_item_poll(epi, &epq.pt, 1); + + /* + * We have to check if something went wrong during the poll wait queue + * install process. Namely an allocation for a wait queue failed due + * high memory pressure. + */ + if (unlikely(!epq.epi)) { + ep_remove(ep, epi); + return -ENOMEM; + } + + /* We have to drop the new item inside our item list to keep track of it */ + write_lock_irq(&ep->lock); + + /* record NAPI ID of new item if present */ + ep_set_busy_poll_napi_id(epi); + + /* If the file is already "ready" we drop it inside the ready list */ + if (revents && !ep_is_linked(epi)) { + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + + /* Notify waiting tasks that events are available */ + if (waitqueue_active(&ep->wq)) + wake_up(&ep->wq); + if (waitqueue_active(&ep->poll_wait)) + pwake++; + } + + write_unlock_irq(&ep->lock); + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(ep, NULL, 0); + + return 0; +} + +/* + * Modify the interest event mask by dropping an event if the new mask + * has a match in the current file status. Must be called with "mtx" held. + */ +static int ep_modify(struct eventpoll *ep, struct epitem *epi, + const struct epoll_event *event) +{ + int pwake = 0; + poll_table pt; + + lockdep_assert_irqs_enabled(); + + init_poll_funcptr(&pt, NULL); + + /* + * Set the new event interest mask before calling f_op->poll(); + * otherwise we might miss an event that happens between the + * f_op->poll() call and the new event set registering. + */ + epi->event.events = event->events; /* need barrier below */ + epi->event.data = event->data; /* protected by mtx */ + if (epi->event.events & EPOLLWAKEUP) { + if (!ep_has_wakeup_source(epi)) + ep_create_wakeup_source(epi); + } else if (ep_has_wakeup_source(epi)) { + ep_destroy_wakeup_source(epi); + } + + /* + * The following barrier has two effects: + * + * 1) Flush epi changes above to other CPUs. This ensures + * we do not miss events from ep_poll_callback if an + * event occurs immediately after we call f_op->poll(). + * We need this because we did not take ep->lock while + * changing epi above (but ep_poll_callback does take + * ep->lock). + * + * 2) We also need to ensure we do not miss _past_ events + * when calling f_op->poll(). This barrier also + * pairs with the barrier in wq_has_sleeper (see + * comments for wq_has_sleeper). + * + * This barrier will now guarantee ep_poll_callback or f_op->poll + * (or both) will notice the readiness of an item. + */ + smp_mb(); + + /* + * Get current event bits. We can safely use the file* here because + * its usage count has been increased by the caller of this function. + * If the item is "hot" and it is not registered inside the ready + * list, push it inside. + */ + if (ep_item_poll(epi, &pt, 1)) { + write_lock_irq(&ep->lock); + if (!ep_is_linked(epi)) { + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + + /* Notify waiting tasks that events are available */ + if (waitqueue_active(&ep->wq)) + wake_up(&ep->wq); + if (waitqueue_active(&ep->poll_wait)) + pwake++; + } + write_unlock_irq(&ep->lock); + } + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(ep, NULL, 0); + + return 0; +} + +static int ep_send_events(struct eventpoll *ep, + struct epoll_event __user *events, int maxevents) +{ + struct epitem *epi, *tmp; + LIST_HEAD(txlist); + poll_table pt; + int res = 0; + + /* + * Always short-circuit for fatal signals to allow threads to make a + * timely exit without the chance of finding more events available and + * fetching repeatedly. + */ + if (fatal_signal_pending(current)) + return -EINTR; + + init_poll_funcptr(&pt, NULL); + + mutex_lock(&ep->mtx); + ep_start_scan(ep, &txlist); + + /* + * We can loop without lock because we are passed a task private list. + * Items cannot vanish during the loop we are holding ep->mtx. + */ + list_for_each_entry_safe(epi, tmp, &txlist, rdllink) { + struct wakeup_source *ws; + __poll_t revents; + + if (res >= maxevents) + break; + + /* + * Activate ep->ws before deactivating epi->ws to prevent + * triggering auto-suspend here (in case we reactive epi->ws + * below). + * + * This could be rearranged to delay the deactivation of epi->ws + * instead, but then epi->ws would temporarily be out of sync + * with ep_is_linked(). + */ + ws = ep_wakeup_source(epi); + if (ws) { + if (ws->active) + __pm_stay_awake(ep->ws); + __pm_relax(ws); + } + + list_del_init(&epi->rdllink); + + /* + * If the event mask intersect the caller-requested one, + * deliver the event to userspace. Again, we are holding ep->mtx, + * so no operations coming from userspace can change the item. + */ + revents = ep_item_poll(epi, &pt, 1); + if (!revents) + continue; + + events = epoll_put_uevent(revents, epi->event.data, events); + if (!events) { + list_add(&epi->rdllink, &txlist); + ep_pm_stay_awake(epi); + if (!res) + res = -EFAULT; + break; + } + res++; + if (epi->event.events & EPOLLONESHOT) + epi->event.events &= EP_PRIVATE_BITS; + else if (!(epi->event.events & EPOLLET)) { + /* + * If this file has been added with Level + * Trigger mode, we need to insert back inside + * the ready list, so that the next call to + * epoll_wait() will check again the events + * availability. At this point, no one can insert + * into ep->rdllist besides us. The epoll_ctl() + * callers are locked out by + * ep_scan_ready_list() holding "mtx" and the + * poll callback will queue them in ep->ovflist. + */ + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + } + } + ep_done_scan(ep, &txlist); + mutex_unlock(&ep->mtx); + + return res; +} + +static struct timespec64 *ep_timeout_to_timespec(struct timespec64 *to, long ms) +{ + struct timespec64 now; + + if (ms < 0) + return NULL; + + if (!ms) { + to->tv_sec = 0; + to->tv_nsec = 0; + return to; + } + + to->tv_sec = ms / MSEC_PER_SEC; + to->tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC); + + ktime_get_ts64(&now); + *to = timespec64_add_safe(now, *to); + return to; +} + +/* + * autoremove_wake_function, but remove even on failure to wake up, because we + * know that default_wake_function/ttwu will only fail if the thread is already + * woken, and in that case the ep_poll loop will remove the entry anyways, not + * try to reuse it. + */ +static int ep_autoremove_wake_function(struct wait_queue_entry *wq_entry, + unsigned int mode, int sync, void *key) +{ + int ret = default_wake_function(wq_entry, mode, sync, key); + + /* + * Pairs with list_empty_careful in ep_poll, and ensures future loop + * iterations see the cause of this wakeup. + */ + list_del_init_careful(&wq_entry->entry); + return ret; +} + +/** + * ep_poll - Retrieves ready events, and delivers them to the caller-supplied + * event buffer. + * + * @ep: Pointer to the eventpoll context. + * @events: Pointer to the userspace buffer where the ready events should be + * stored. + * @maxevents: Size (in terms of number of events) of the caller event buffer. + * @timeout: Maximum timeout for the ready events fetch operation, in + * timespec. If the timeout is zero, the function will not block, + * while if the @timeout ptr is NULL, the function will block + * until at least one event has been retrieved (or an error + * occurred). + * + * Return: the number of ready events which have been fetched, or an + * error code, in case of error. + */ +static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, + int maxevents, struct timespec64 *timeout) +{ + int res, eavail, timed_out = 0; + u64 slack = 0; + wait_queue_entry_t wait; + ktime_t expires, *to = NULL; + + lockdep_assert_irqs_enabled(); + + if (timeout && (timeout->tv_sec | timeout->tv_nsec)) { + slack = select_estimate_accuracy(timeout); + to = &expires; + *to = timespec64_to_ktime(*timeout); + } else if (timeout) { + /* + * Avoid the unnecessary trip to the wait queue loop, if the + * caller specified a non blocking operation. + */ + timed_out = 1; + } + + /* + * This call is racy: We may or may not see events that are being added + * to the ready list under the lock (e.g., in IRQ callbacks). For cases + * with a non-zero timeout, this thread will check the ready list under + * lock and will add to the wait queue. For cases with a zero + * timeout, the user by definition should not care and will have to + * recheck again. + */ + eavail = ep_events_available(ep); + + while (1) { + if (eavail) { + /* + * Try to transfer events to user space. In case we get + * 0 events and there's still timeout left over, we go + * trying again in search of more luck. + */ + res = ep_send_events(ep, events, maxevents); + if (res) + return res; + } + + if (timed_out) + return 0; + + eavail = ep_busy_loop(ep, timed_out); + if (eavail) + continue; + + if (signal_pending(current)) + return -EINTR; + + /* + * Internally init_wait() uses autoremove_wake_function(), + * thus wait entry is removed from the wait queue on each + * wakeup. Why it is important? In case of several waiters + * each new wakeup will hit the next waiter, giving it the + * chance to harvest new event. Otherwise wakeup can be + * lost. This is also good performance-wise, because on + * normal wakeup path no need to call __remove_wait_queue() + * explicitly, thus ep->lock is not taken, which halts the + * event delivery. + * + * In fact, we now use an even more aggressive function that + * unconditionally removes, because we don't reuse the wait + * entry between loop iterations. This lets us also avoid the + * performance issue if a process is killed, causing all of its + * threads to wake up without being removed normally. + */ + init_wait(&wait); + wait.func = ep_autoremove_wake_function; + + write_lock_irq(&ep->lock); + /* + * Barrierless variant, waitqueue_active() is called under + * the same lock on wakeup ep_poll_callback() side, so it + * is safe to avoid an explicit barrier. + */ + __set_current_state(TASK_INTERRUPTIBLE); + + /* + * Do the final check under the lock. ep_scan_ready_list() + * plays with two lists (->rdllist and ->ovflist) and there + * is always a race when both lists are empty for short + * period of time although events are pending, so lock is + * important. + */ + eavail = ep_events_available(ep); + if (!eavail) + __add_wait_queue_exclusive(&ep->wq, &wait); + + write_unlock_irq(&ep->lock); + + if (!eavail) + timed_out = !schedule_hrtimeout_range(to, slack, + HRTIMER_MODE_ABS); + __set_current_state(TASK_RUNNING); + + /* + * We were woken up, thus go and try to harvest some events. + * If timed out and still on the wait queue, recheck eavail + * carefully under lock, below. + */ + eavail = 1; + + if (!list_empty_careful(&wait.entry)) { + write_lock_irq(&ep->lock); + /* + * If the thread timed out and is not on the wait queue, + * it means that the thread was woken up after its + * timeout expired before it could reacquire the lock. + * Thus, when wait.entry is empty, it needs to harvest + * events. + */ + if (timed_out) + eavail = list_empty(&wait.entry); + __remove_wait_queue(&ep->wq, &wait); + write_unlock_irq(&ep->lock); + } + } +} + +/** + * ep_loop_check_proc - verify that adding an epoll file inside another + * epoll structure does not violate the constraints, in + * terms of closed loops, or too deep chains (which can + * result in excessive stack usage). + * + * @ep: the &struct eventpoll to be currently checked. + * @depth: Current depth of the path being checked. + * + * Return: %zero if adding the epoll @file inside current epoll + * structure @ep does not violate the constraints, or %-1 otherwise. + */ +static int ep_loop_check_proc(struct eventpoll *ep, int depth) +{ + int error = 0; + struct rb_node *rbp; + struct epitem *epi; + + mutex_lock_nested(&ep->mtx, depth + 1); + ep->gen = loop_check_gen; + for (rbp = rb_first_cached(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + if (unlikely(is_file_epoll(epi->ffd.file))) { + struct eventpoll *ep_tovisit; + ep_tovisit = epi->ffd.file->private_data; + if (ep_tovisit->gen == loop_check_gen) + continue; + if (ep_tovisit == inserting_into || depth > EP_MAX_NESTS) + error = -1; + else + error = ep_loop_check_proc(ep_tovisit, depth + 1); + if (error != 0) + break; + } else { + /* + * If we've reached a file that is not associated with + * an ep, then we need to check if the newly added + * links are going to add too many wakeup paths. We do + * this by adding it to the tfile_check_list, if it's + * not already there, and calling reverse_path_check() + * during ep_insert(). + */ + list_file(epi->ffd.file); + } + } + mutex_unlock(&ep->mtx); + + return error; +} + +/** + * ep_loop_check - Performs a check to verify that adding an epoll file (@to) + * into another epoll file (represented by @ep) does not create + * closed loops or too deep chains. + * + * @ep: Pointer to the epoll we are inserting into. + * @to: Pointer to the epoll to be inserted. + * + * Return: %zero if adding the epoll @to inside the epoll @from + * does not violate the constraints, or %-1 otherwise. + */ +static int ep_loop_check(struct eventpoll *ep, struct eventpoll *to) +{ + inserting_into = ep; + return ep_loop_check_proc(to, 0); +} + +static void clear_tfile_check_list(void) +{ + rcu_read_lock(); + while (tfile_check_list != EP_UNACTIVE_PTR) { + struct epitems_head *head = tfile_check_list; + tfile_check_list = head->next; + unlist_file(head); + } + rcu_read_unlock(); +} + +/* + * Open an eventpoll file descriptor. + */ +static int do_epoll_create(int flags) +{ + int error, fd; + struct eventpoll *ep = NULL; + struct file *file; + + /* Check the EPOLL_* constant for consistency. */ + BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC); + + if (flags & ~EPOLL_CLOEXEC) + return -EINVAL; + /* + * Create the internal data structure ("struct eventpoll"). + */ + error = ep_alloc(&ep); + if (error < 0) + return error; + /* + * Creates all the items needed to setup an eventpoll file. That is, + * a file structure and a free file descriptor. + */ + fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC)); + if (fd < 0) { + error = fd; + goto out_free_ep; + } + file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep, + O_RDWR | (flags & O_CLOEXEC)); + if (IS_ERR(file)) { + error = PTR_ERR(file); + goto out_free_fd; + } + ep->file = file; + fd_install(fd, file); + return fd; + +out_free_fd: + put_unused_fd(fd); +out_free_ep: + ep_free(ep); + return error; +} + +SYSCALL_DEFINE1(epoll_create1, int, flags) +{ + return do_epoll_create(flags); +} + +SYSCALL_DEFINE1(epoll_create, int, size) +{ + if (size <= 0) + return -EINVAL; + + return do_epoll_create(0); +} + +static inline int epoll_mutex_lock(struct mutex *mutex, int depth, + bool nonblock) +{ + if (!nonblock) { + mutex_lock_nested(mutex, depth); + return 0; + } + if (mutex_trylock(mutex)) + return 0; + return -EAGAIN; +} + +int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds, + bool nonblock) +{ + int error; + int full_check = 0; + struct fd f, tf; + struct eventpoll *ep; + struct epitem *epi; + struct eventpoll *tep = NULL; + + error = -EBADF; + f = fdget(epfd); + if (!f.file) + goto error_return; + + /* Get the "struct file *" for the target file */ + tf = fdget(fd); + if (!tf.file) + goto error_fput; + + /* The target file descriptor must support poll */ + error = -EPERM; + if (!file_can_poll(tf.file)) + goto error_tgt_fput; + + /* Check if EPOLLWAKEUP is allowed */ + if (ep_op_has_event(op)) + ep_take_care_of_epollwakeup(epds); + + /* + * We have to check that the file structure underneath the file descriptor + * the user passed to us _is_ an eventpoll file. And also we do not permit + * adding an epoll file descriptor inside itself. + */ + error = -EINVAL; + if (f.file == tf.file || !is_file_epoll(f.file)) + goto error_tgt_fput; + + /* + * epoll adds to the wakeup queue at EPOLL_CTL_ADD time only, + * so EPOLLEXCLUSIVE is not allowed for a EPOLL_CTL_MOD operation. + * Also, we do not currently supported nested exclusive wakeups. + */ + if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) { + if (op == EPOLL_CTL_MOD) + goto error_tgt_fput; + if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) || + (epds->events & ~EPOLLEXCLUSIVE_OK_BITS))) + goto error_tgt_fput; + } + + /* + * At this point it is safe to assume that the "private_data" contains + * our own data structure. + */ + ep = f.file->private_data; + + /* + * When we insert an epoll file descriptor inside another epoll file + * descriptor, there is the chance of creating closed loops, which are + * better be handled here, than in more critical paths. While we are + * checking for loops we also determine the list of files reachable + * and hang them on the tfile_check_list, so we can check that we + * haven't created too many possible wakeup paths. + * + * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when + * the epoll file descriptor is attaching directly to a wakeup source, + * unless the epoll file descriptor is nested. The purpose of taking the + * 'epmutex' on add is to prevent complex toplogies such as loops and + * deep wakeup paths from forming in parallel through multiple + * EPOLL_CTL_ADD operations. + */ + error = epoll_mutex_lock(&ep->mtx, 0, nonblock); + if (error) + goto error_tgt_fput; + if (op == EPOLL_CTL_ADD) { + if (READ_ONCE(f.file->f_ep) || ep->gen == loop_check_gen || + is_file_epoll(tf.file)) { + mutex_unlock(&ep->mtx); + error = epoll_mutex_lock(&epmutex, 0, nonblock); + if (error) + goto error_tgt_fput; + loop_check_gen++; + full_check = 1; + if (is_file_epoll(tf.file)) { + tep = tf.file->private_data; + error = -ELOOP; + if (ep_loop_check(ep, tep) != 0) + goto error_tgt_fput; + } + error = epoll_mutex_lock(&ep->mtx, 0, nonblock); + if (error) + goto error_tgt_fput; + } + } + + /* + * Try to lookup the file inside our RB tree. Since we grabbed "mtx" + * above, we can be sure to be able to use the item looked up by + * ep_find() till we release the mutex. + */ + epi = ep_find(ep, tf.file, fd); + + error = -EINVAL; + switch (op) { + case EPOLL_CTL_ADD: + if (!epi) { + epds->events |= EPOLLERR | EPOLLHUP; + error = ep_insert(ep, epds, tf.file, fd, full_check); + } else + error = -EEXIST; + break; + case EPOLL_CTL_DEL: + if (epi) + error = ep_remove(ep, epi); + else + error = -ENOENT; + break; + case EPOLL_CTL_MOD: + if (epi) { + if (!(epi->event.events & EPOLLEXCLUSIVE)) { + epds->events |= EPOLLERR | EPOLLHUP; + error = ep_modify(ep, epi, epds); + } + } else + error = -ENOENT; + break; + } + mutex_unlock(&ep->mtx); + +error_tgt_fput: + if (full_check) { + clear_tfile_check_list(); + loop_check_gen++; + mutex_unlock(&epmutex); + } + + fdput(tf); +error_fput: + fdput(f); +error_return: + + return error; +} + +/* + * The following function implements the controller interface for + * the eventpoll file that enables the insertion/removal/change of + * file descriptors inside the interest set. + */ +SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, + struct epoll_event __user *, event) +{ + struct epoll_event epds; + + if (ep_op_has_event(op) && + copy_from_user(&epds, event, sizeof(struct epoll_event))) + return -EFAULT; + + return do_epoll_ctl(epfd, op, fd, &epds, false); +} + +/* + * Implement the event wait interface for the eventpoll file. It is the kernel + * part of the user space epoll_wait(2). + */ +static int do_epoll_wait(int epfd, struct epoll_event __user *events, + int maxevents, struct timespec64 *to) +{ + int error; + struct fd f; + struct eventpoll *ep; + + /* The maximum number of event must be greater than zero */ + if (maxevents <= 0 || maxevents > EP_MAX_EVENTS) + return -EINVAL; + + /* Verify that the area passed by the user is writeable */ + if (!access_ok(events, maxevents * sizeof(struct epoll_event))) + return -EFAULT; + + /* Get the "struct file *" for the eventpoll file */ + f = fdget(epfd); + if (!f.file) + return -EBADF; + + /* + * We have to check that the file structure underneath the fd + * the user passed to us _is_ an eventpoll file. + */ + error = -EINVAL; + if (!is_file_epoll(f.file)) + goto error_fput; + + /* + * At this point it is safe to assume that the "private_data" contains + * our own data structure. + */ + ep = f.file->private_data; + + /* Time to fish for events ... */ + error = ep_poll(ep, events, maxevents, to); + +error_fput: + fdput(f); + return error; +} + +SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, + int, maxevents, int, timeout) +{ + struct timespec64 to; + + return do_epoll_wait(epfd, events, maxevents, + ep_timeout_to_timespec(&to, timeout)); +} + +/* + * Implement the event wait interface for the eventpoll file. It is the kernel + * part of the user space epoll_pwait(2). + */ +static int do_epoll_pwait(int epfd, struct epoll_event __user *events, + int maxevents, struct timespec64 *to, + const sigset_t __user *sigmask, size_t sigsetsize) +{ + int error; + + /* + * If the caller wants a certain signal mask to be set during the wait, + * we apply it here. + */ + error = set_user_sigmask(sigmask, sigsetsize); + if (error) + return error; + + error = do_epoll_wait(epfd, events, maxevents, to); + + restore_saved_sigmask_unless(error == -EINTR); + + return error; +} + +SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events, + int, maxevents, int, timeout, const sigset_t __user *, sigmask, + size_t, sigsetsize) +{ + struct timespec64 to; + + return do_epoll_pwait(epfd, events, maxevents, + ep_timeout_to_timespec(&to, timeout), + sigmask, sigsetsize); +} + +SYSCALL_DEFINE6(epoll_pwait2, int, epfd, struct epoll_event __user *, events, + int, maxevents, const struct __kernel_timespec __user *, timeout, + const sigset_t __user *, sigmask, size_t, sigsetsize) +{ + struct timespec64 ts, *to = NULL; + + if (timeout) { + if (get_timespec64(&ts, timeout)) + return -EFAULT; + to = &ts; + if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) + return -EINVAL; + } + + return do_epoll_pwait(epfd, events, maxevents, to, + sigmask, sigsetsize); +} + +#ifdef CONFIG_COMPAT +static int do_compat_epoll_pwait(int epfd, struct epoll_event __user *events, + int maxevents, struct timespec64 *timeout, + const compat_sigset_t __user *sigmask, + compat_size_t sigsetsize) +{ + long err; + + /* + * If the caller wants a certain signal mask to be set during the wait, + * we apply it here. + */ + err = set_compat_user_sigmask(sigmask, sigsetsize); + if (err) + return err; + + err = do_epoll_wait(epfd, events, maxevents, timeout); + + restore_saved_sigmask_unless(err == -EINTR); + + return err; +} + +COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd, + struct epoll_event __user *, events, + int, maxevents, int, timeout, + const compat_sigset_t __user *, sigmask, + compat_size_t, sigsetsize) +{ + struct timespec64 to; + + return do_compat_epoll_pwait(epfd, events, maxevents, + ep_timeout_to_timespec(&to, timeout), + sigmask, sigsetsize); +} + +COMPAT_SYSCALL_DEFINE6(epoll_pwait2, int, epfd, + struct epoll_event __user *, events, + int, maxevents, + const struct __kernel_timespec __user *, timeout, + const compat_sigset_t __user *, sigmask, + compat_size_t, sigsetsize) +{ + struct timespec64 ts, *to = NULL; + + if (timeout) { + if (get_timespec64(&ts, timeout)) + return -EFAULT; + to = &ts; + if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) + return -EINVAL; + } + + return do_compat_epoll_pwait(epfd, events, maxevents, to, + sigmask, sigsetsize); +} + +#endif + +static int __init eventpoll_init(void) +{ + struct sysinfo si; + + si_meminfo(&si); + /* + * Allows top 4% of lomem to be allocated for epoll watches (per user). + */ + max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) / + EP_ITEM_COST; + BUG_ON(max_user_watches < 0); + + /* + * We can have many thousands of epitems, so prevent this from + * using an extra cache line on 64-bit (and smaller) CPUs + */ + BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128); + + /* Allocates slab cache used to allocate "struct epitem" items */ + epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), + 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL); + + /* Allocates slab cache used to allocate "struct eppoll_entry" */ + pwq_cache = kmem_cache_create("eventpoll_pwq", + sizeof(struct eppoll_entry), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); + epoll_sysctls_init(); + + ephead_cache = kmem_cache_create("ep_head", + sizeof(struct epitems_head), 0, SLAB_PANIC|SLAB_ACCOUNT, NULL); + + return 0; +} +fs_initcall(eventpoll_init); |