summaryrefslogtreecommitdiffstats
path: root/fs/eventfd.c
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /fs/eventfd.c
parentInitial commit. (diff)
downloadlinux-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/eventfd.c')
-rw-r--r--fs/eventfd.c467
1 files changed, 467 insertions, 0 deletions
diff --git a/fs/eventfd.c b/fs/eventfd.c
new file mode 100644
index 000000000..4a60ea932
--- /dev/null
+++ b/fs/eventfd.c
@@ -0,0 +1,467 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * fs/eventfd.c
+ *
+ * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#include <linux/file.h>
+#include <linux/poll.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/sched/signal.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/anon_inodes.h>
+#include <linux/syscalls.h>
+#include <linux/export.h>
+#include <linux/kref.h>
+#include <linux/eventfd.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/idr.h>
+#include <linux/uio.h>
+
+static DEFINE_IDA(eventfd_ida);
+
+struct eventfd_ctx {
+ struct kref kref;
+ wait_queue_head_t wqh;
+ /*
+ * Every time that a write(2) is performed on an eventfd, the
+ * value of the __u64 being written is added to "count" and a
+ * wakeup is performed on "wqh". A read(2) will return the "count"
+ * value to userspace, and will reset "count" to zero. The kernel
+ * side eventfd_signal() also, adds to the "count" counter and
+ * issue a wakeup.
+ */
+ __u64 count;
+ unsigned int flags;
+ int id;
+};
+
+__u64 eventfd_signal_mask(struct eventfd_ctx *ctx, __u64 n, unsigned mask)
+{
+ unsigned long flags;
+
+ /*
+ * Deadlock or stack overflow issues can happen if we recurse here
+ * through waitqueue wakeup handlers. If the caller users potentially
+ * nested waitqueues with custom wakeup handlers, then it should
+ * check eventfd_signal_allowed() before calling this function. If
+ * it returns false, the eventfd_signal() call should be deferred to a
+ * safe context.
+ */
+ if (WARN_ON_ONCE(current->in_eventfd))
+ return 0;
+
+ spin_lock_irqsave(&ctx->wqh.lock, flags);
+ current->in_eventfd = 1;
+ if (ULLONG_MAX - ctx->count < n)
+ n = ULLONG_MAX - ctx->count;
+ ctx->count += n;
+ if (waitqueue_active(&ctx->wqh))
+ wake_up_locked_poll(&ctx->wqh, EPOLLIN | mask);
+ current->in_eventfd = 0;
+ spin_unlock_irqrestore(&ctx->wqh.lock, flags);
+
+ return n;
+}
+
+/**
+ * eventfd_signal - Adds @n to the eventfd counter.
+ * @ctx: [in] Pointer to the eventfd context.
+ * @n: [in] Value of the counter to be added to the eventfd internal counter.
+ * The value cannot be negative.
+ *
+ * This function is supposed to be called by the kernel in paths that do not
+ * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
+ * value, and we signal this as overflow condition by returning a EPOLLERR
+ * to poll(2).
+ *
+ * Returns the amount by which the counter was incremented. This will be less
+ * than @n if the counter has overflowed.
+ */
+__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
+{
+ return eventfd_signal_mask(ctx, n, 0);
+}
+EXPORT_SYMBOL_GPL(eventfd_signal);
+
+static void eventfd_free_ctx(struct eventfd_ctx *ctx)
+{
+ if (ctx->id >= 0)
+ ida_simple_remove(&eventfd_ida, ctx->id);
+ kfree(ctx);
+}
+
+static void eventfd_free(struct kref *kref)
+{
+ struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
+
+ eventfd_free_ctx(ctx);
+}
+
+/**
+ * eventfd_ctx_put - Releases a reference to the internal eventfd context.
+ * @ctx: [in] Pointer to eventfd context.
+ *
+ * The eventfd context reference must have been previously acquired either
+ * with eventfd_ctx_fdget() or eventfd_ctx_fileget().
+ */
+void eventfd_ctx_put(struct eventfd_ctx *ctx)
+{
+ kref_put(&ctx->kref, eventfd_free);
+}
+EXPORT_SYMBOL_GPL(eventfd_ctx_put);
+
+static int eventfd_release(struct inode *inode, struct file *file)
+{
+ struct eventfd_ctx *ctx = file->private_data;
+
+ wake_up_poll(&ctx->wqh, EPOLLHUP);
+ eventfd_ctx_put(ctx);
+ return 0;
+}
+
+static __poll_t eventfd_poll(struct file *file, poll_table *wait)
+{
+ struct eventfd_ctx *ctx = file->private_data;
+ __poll_t events = 0;
+ u64 count;
+
+ poll_wait(file, &ctx->wqh, wait);
+
+ /*
+ * All writes to ctx->count occur within ctx->wqh.lock. This read
+ * can be done outside ctx->wqh.lock because we know that poll_wait
+ * takes that lock (through add_wait_queue) if our caller will sleep.
+ *
+ * The read _can_ therefore seep into add_wait_queue's critical
+ * section, but cannot move above it! add_wait_queue's spin_lock acts
+ * as an acquire barrier and ensures that the read be ordered properly
+ * against the writes. The following CAN happen and is safe:
+ *
+ * poll write
+ * ----------------- ------------
+ * lock ctx->wqh.lock (in poll_wait)
+ * count = ctx->count
+ * __add_wait_queue
+ * unlock ctx->wqh.lock
+ * lock ctx->qwh.lock
+ * ctx->count += n
+ * if (waitqueue_active)
+ * wake_up_locked_poll
+ * unlock ctx->qwh.lock
+ * eventfd_poll returns 0
+ *
+ * but the following, which would miss a wakeup, cannot happen:
+ *
+ * poll write
+ * ----------------- ------------
+ * count = ctx->count (INVALID!)
+ * lock ctx->qwh.lock
+ * ctx->count += n
+ * **waitqueue_active is false**
+ * **no wake_up_locked_poll!**
+ * unlock ctx->qwh.lock
+ * lock ctx->wqh.lock (in poll_wait)
+ * __add_wait_queue
+ * unlock ctx->wqh.lock
+ * eventfd_poll returns 0
+ */
+ count = READ_ONCE(ctx->count);
+
+ if (count > 0)
+ events |= EPOLLIN;
+ if (count == ULLONG_MAX)
+ events |= EPOLLERR;
+ if (ULLONG_MAX - 1 > count)
+ events |= EPOLLOUT;
+
+ return events;
+}
+
+void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
+{
+ lockdep_assert_held(&ctx->wqh.lock);
+
+ *cnt = ((ctx->flags & EFD_SEMAPHORE) && ctx->count) ? 1 : ctx->count;
+ ctx->count -= *cnt;
+}
+EXPORT_SYMBOL_GPL(eventfd_ctx_do_read);
+
+/**
+ * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
+ * @ctx: [in] Pointer to eventfd context.
+ * @wait: [in] Wait queue to be removed.
+ * @cnt: [out] Pointer to the 64-bit counter value.
+ *
+ * Returns %0 if successful, or the following error codes:
+ *
+ * -EAGAIN : The operation would have blocked.
+ *
+ * This is used to atomically remove a wait queue entry from the eventfd wait
+ * queue head, and read/reset the counter value.
+ */
+int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait,
+ __u64 *cnt)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&ctx->wqh.lock, flags);
+ eventfd_ctx_do_read(ctx, cnt);
+ __remove_wait_queue(&ctx->wqh, wait);
+ if (*cnt != 0 && waitqueue_active(&ctx->wqh))
+ wake_up_locked_poll(&ctx->wqh, EPOLLOUT);
+ spin_unlock_irqrestore(&ctx->wqh.lock, flags);
+
+ return *cnt != 0 ? 0 : -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
+
+static ssize_t eventfd_read(struct kiocb *iocb, struct iov_iter *to)
+{
+ struct file *file = iocb->ki_filp;
+ struct eventfd_ctx *ctx = file->private_data;
+ __u64 ucnt = 0;
+ DECLARE_WAITQUEUE(wait, current);
+
+ if (iov_iter_count(to) < sizeof(ucnt))
+ return -EINVAL;
+ spin_lock_irq(&ctx->wqh.lock);
+ if (!ctx->count) {
+ if ((file->f_flags & O_NONBLOCK) ||
+ (iocb->ki_flags & IOCB_NOWAIT)) {
+ spin_unlock_irq(&ctx->wqh.lock);
+ return -EAGAIN;
+ }
+ __add_wait_queue(&ctx->wqh, &wait);
+ for (;;) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (ctx->count)
+ break;
+ if (signal_pending(current)) {
+ __remove_wait_queue(&ctx->wqh, &wait);
+ __set_current_state(TASK_RUNNING);
+ spin_unlock_irq(&ctx->wqh.lock);
+ return -ERESTARTSYS;
+ }
+ spin_unlock_irq(&ctx->wqh.lock);
+ schedule();
+ spin_lock_irq(&ctx->wqh.lock);
+ }
+ __remove_wait_queue(&ctx->wqh, &wait);
+ __set_current_state(TASK_RUNNING);
+ }
+ eventfd_ctx_do_read(ctx, &ucnt);
+ current->in_eventfd = 1;
+ if (waitqueue_active(&ctx->wqh))
+ wake_up_locked_poll(&ctx->wqh, EPOLLOUT);
+ current->in_eventfd = 0;
+ spin_unlock_irq(&ctx->wqh.lock);
+ if (unlikely(copy_to_iter(&ucnt, sizeof(ucnt), to) != sizeof(ucnt)))
+ return -EFAULT;
+
+ return sizeof(ucnt);
+}
+
+static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
+ loff_t *ppos)
+{
+ struct eventfd_ctx *ctx = file->private_data;
+ ssize_t res;
+ __u64 ucnt;
+ DECLARE_WAITQUEUE(wait, current);
+
+ if (count < sizeof(ucnt))
+ return -EINVAL;
+ if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
+ return -EFAULT;
+ if (ucnt == ULLONG_MAX)
+ return -EINVAL;
+ spin_lock_irq(&ctx->wqh.lock);
+ res = -EAGAIN;
+ if (ULLONG_MAX - ctx->count > ucnt)
+ res = sizeof(ucnt);
+ else if (!(file->f_flags & O_NONBLOCK)) {
+ __add_wait_queue(&ctx->wqh, &wait);
+ for (res = 0;;) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (ULLONG_MAX - ctx->count > ucnt) {
+ res = sizeof(ucnt);
+ break;
+ }
+ if (signal_pending(current)) {
+ res = -ERESTARTSYS;
+ break;
+ }
+ spin_unlock_irq(&ctx->wqh.lock);
+ schedule();
+ spin_lock_irq(&ctx->wqh.lock);
+ }
+ __remove_wait_queue(&ctx->wqh, &wait);
+ __set_current_state(TASK_RUNNING);
+ }
+ if (likely(res > 0)) {
+ ctx->count += ucnt;
+ current->in_eventfd = 1;
+ if (waitqueue_active(&ctx->wqh))
+ wake_up_locked_poll(&ctx->wqh, EPOLLIN);
+ current->in_eventfd = 0;
+ }
+ spin_unlock_irq(&ctx->wqh.lock);
+
+ return res;
+}
+
+#ifdef CONFIG_PROC_FS
+static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+ struct eventfd_ctx *ctx = f->private_data;
+
+ spin_lock_irq(&ctx->wqh.lock);
+ seq_printf(m, "eventfd-count: %16llx\n",
+ (unsigned long long)ctx->count);
+ spin_unlock_irq(&ctx->wqh.lock);
+ seq_printf(m, "eventfd-id: %d\n", ctx->id);
+}
+#endif
+
+static const struct file_operations eventfd_fops = {
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = eventfd_show_fdinfo,
+#endif
+ .release = eventfd_release,
+ .poll = eventfd_poll,
+ .read_iter = eventfd_read,
+ .write = eventfd_write,
+ .llseek = noop_llseek,
+};
+
+/**
+ * eventfd_fget - Acquire a reference of an eventfd file descriptor.
+ * @fd: [in] Eventfd file descriptor.
+ *
+ * Returns a pointer to the eventfd file structure in case of success, or the
+ * following error pointer:
+ *
+ * -EBADF : Invalid @fd file descriptor.
+ * -EINVAL : The @fd file descriptor is not an eventfd file.
+ */
+struct file *eventfd_fget(int fd)
+{
+ struct file *file;
+
+ file = fget(fd);
+ if (!file)
+ return ERR_PTR(-EBADF);
+ if (file->f_op != &eventfd_fops) {
+ fput(file);
+ return ERR_PTR(-EINVAL);
+ }
+
+ return file;
+}
+EXPORT_SYMBOL_GPL(eventfd_fget);
+
+/**
+ * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
+ * @fd: [in] Eventfd file descriptor.
+ *
+ * Returns a pointer to the internal eventfd context, otherwise the error
+ * pointers returned by the following functions:
+ *
+ * eventfd_fget
+ */
+struct eventfd_ctx *eventfd_ctx_fdget(int fd)
+{
+ struct eventfd_ctx *ctx;
+ struct fd f = fdget(fd);
+ if (!f.file)
+ return ERR_PTR(-EBADF);
+ ctx = eventfd_ctx_fileget(f.file);
+ fdput(f);
+ return ctx;
+}
+EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
+
+/**
+ * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
+ * @file: [in] Eventfd file pointer.
+ *
+ * Returns a pointer to the internal eventfd context, otherwise the error
+ * pointer:
+ *
+ * -EINVAL : The @fd file descriptor is not an eventfd file.
+ */
+struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
+{
+ struct eventfd_ctx *ctx;
+
+ if (file->f_op != &eventfd_fops)
+ return ERR_PTR(-EINVAL);
+
+ ctx = file->private_data;
+ kref_get(&ctx->kref);
+ return ctx;
+}
+EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
+
+static int do_eventfd(unsigned int count, int flags)
+{
+ struct eventfd_ctx *ctx;
+ struct file *file;
+ int fd;
+
+ /* Check the EFD_* constants for consistency. */
+ BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
+ BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
+
+ if (flags & ~EFD_FLAGS_SET)
+ return -EINVAL;
+
+ ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
+ if (!ctx)
+ return -ENOMEM;
+
+ kref_init(&ctx->kref);
+ init_waitqueue_head(&ctx->wqh);
+ ctx->count = count;
+ ctx->flags = flags;
+ ctx->id = ida_simple_get(&eventfd_ida, 0, 0, GFP_KERNEL);
+
+ flags &= EFD_SHARED_FCNTL_FLAGS;
+ flags |= O_RDWR;
+ fd = get_unused_fd_flags(flags);
+ if (fd < 0)
+ goto err;
+
+ file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, flags);
+ if (IS_ERR(file)) {
+ put_unused_fd(fd);
+ fd = PTR_ERR(file);
+ goto err;
+ }
+
+ file->f_mode |= FMODE_NOWAIT;
+ fd_install(fd, file);
+ return fd;
+err:
+ eventfd_free_ctx(ctx);
+ return fd;
+}
+
+SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
+{
+ return do_eventfd(count, flags);
+}
+
+SYSCALL_DEFINE1(eventfd, unsigned int, count)
+{
+ return do_eventfd(count, 0);
+}
+