From: Sebastian Andrzej Siewior Date: Mon, 7 Oct 2019 16:45:18 +0200 Subject: [PATCH 302/353] futex: Make the futex_hash_bucket spinlock_t again and bring back its old state Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=3b3bea588f7b01159f2b0bcab282f896c81489d9 [ Upstream commit 954ad80c23edfe71f4e8ce70b961eac884320c3a ] This is an all-in-one patch that reverts the patches: futex: Make the futex_hash_bucket lock raw futex: Delay deallocation of pi_state and adds back the old patches we had: futex: workaround migrate_disable/enable in different context rtmutex: Handle the various new futex race conditions futex: Fix bug on when a requeued RT task times out futex: Ensure lock/unlock symetry versus pi_lock and hash bucket lock Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt (VMware) --- kernel/futex.c | 228 ++++++++++++++++++-------------- kernel/locking/rtmutex.c | 65 ++++++++- kernel/locking/rtmutex_common.h | 3 + 3 files changed, 193 insertions(+), 103 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 2fc6bedb460e..81090f7a3ed9 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -243,7 +243,7 @@ struct futex_q { struct plist_node list; struct task_struct *task; - raw_spinlock_t *lock_ptr; + spinlock_t *lock_ptr; union futex_key key; struct futex_pi_state *pi_state; struct rt_mutex_waiter *rt_waiter; @@ -264,7 +264,7 @@ static const struct futex_q futex_q_init = { */ struct futex_hash_bucket { atomic_t waiters; - raw_spinlock_t lock; + spinlock_t lock; struct plist_head chain; } ____cacheline_aligned_in_smp; @@ -871,13 +871,13 @@ static void get_pi_state(struct futex_pi_state *pi_state) * Drops a reference to the pi_state object and frees or caches it * when the last reference is gone. */ -static struct futex_pi_state *__put_pi_state(struct futex_pi_state *pi_state) +static void put_pi_state(struct futex_pi_state *pi_state) { if (!pi_state) - return NULL; + return; if (!atomic_dec_and_test(&pi_state->refcount)) - return NULL; + return; /* * If pi_state->owner is NULL, the owner is most probably dying @@ -892,7 +892,9 @@ static struct futex_pi_state *__put_pi_state(struct futex_pi_state *pi_state) raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags); } - if (!current->pi_state_cache) { + if (current->pi_state_cache) { + kfree(pi_state); + } else { /* * pi_state->list is already empty. * clear pi_state->owner. @@ -901,30 +903,6 @@ static struct futex_pi_state *__put_pi_state(struct futex_pi_state *pi_state) pi_state->owner = NULL; atomic_set(&pi_state->refcount, 1); current->pi_state_cache = pi_state; - pi_state = NULL; - } - return pi_state; -} - -static void put_pi_state(struct futex_pi_state *pi_state) -{ - kfree(__put_pi_state(pi_state)); -} - -static void put_pi_state_atomic(struct futex_pi_state *pi_state, - struct list_head *to_free) -{ - if (__put_pi_state(pi_state)) - list_add(&pi_state->list, to_free); -} - -static void free_pi_state_list(struct list_head *to_free) -{ - struct futex_pi_state *p, *next; - - list_for_each_entry_safe(p, next, to_free, list) { - list_del(&p->list); - kfree(p); } } @@ -941,7 +919,6 @@ static void exit_pi_state_list(struct task_struct *curr) struct futex_pi_state *pi_state; struct futex_hash_bucket *hb; union futex_key key = FUTEX_KEY_INIT; - LIST_HEAD(to_free); if (!futex_cmpxchg_enabled) return; @@ -975,7 +952,7 @@ static void exit_pi_state_list(struct task_struct *curr) } raw_spin_unlock_irq(&curr->pi_lock); - raw_spin_lock(&hb->lock); + spin_lock(&hb->lock); raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); raw_spin_lock(&curr->pi_lock); /* @@ -985,8 +962,10 @@ static void exit_pi_state_list(struct task_struct *curr) if (head->next != next) { /* retain curr->pi_lock for the loop invariant */ raw_spin_unlock(&pi_state->pi_mutex.wait_lock); - raw_spin_unlock(&hb->lock); - put_pi_state_atomic(pi_state, &to_free); + raw_spin_unlock_irq(&curr->pi_lock); + spin_unlock(&hb->lock); + raw_spin_lock_irq(&curr->pi_lock); + put_pi_state(pi_state); continue; } @@ -997,7 +976,7 @@ static void exit_pi_state_list(struct task_struct *curr) raw_spin_unlock(&curr->pi_lock); raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); - raw_spin_unlock(&hb->lock); + spin_unlock(&hb->lock); rt_mutex_futex_unlock(&pi_state->pi_mutex); put_pi_state(pi_state); @@ -1005,8 +984,6 @@ static void exit_pi_state_list(struct task_struct *curr) raw_spin_lock_irq(&curr->pi_lock); } raw_spin_unlock_irq(&curr->pi_lock); - - free_pi_state_list(&to_free); } #else static inline void exit_pi_state_list(struct task_struct *curr) { } @@ -1548,7 +1525,7 @@ static void __unqueue_futex(struct futex_q *q) { struct futex_hash_bucket *hb; - if (WARN_ON_SMP(!q->lock_ptr || !raw_spin_is_locked(q->lock_ptr)) + if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr)) || WARN_ON(plist_node_empty(&q->list))) return; @@ -1668,21 +1645,21 @@ static inline void double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) { if (hb1 <= hb2) { - raw_spin_lock(&hb1->lock); + spin_lock(&hb1->lock); if (hb1 < hb2) - raw_spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); + spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING); } else { /* hb1 > hb2 */ - raw_spin_lock(&hb2->lock); - raw_spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); + spin_lock(&hb2->lock); + spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING); } } static inline void double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2) { - raw_spin_unlock(&hb1->lock); + spin_unlock(&hb1->lock); if (hb1 != hb2) - raw_spin_unlock(&hb2->lock); + spin_unlock(&hb2->lock); } /* @@ -1710,7 +1687,7 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) if (!hb_waiters_pending(hb)) goto out_put_key; - raw_spin_lock(&hb->lock); + spin_lock(&hb->lock); plist_for_each_entry_safe(this, next, &hb->chain, list) { if (match_futex (&this->key, &key)) { @@ -1729,7 +1706,7 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) } } - raw_spin_unlock(&hb->lock); + spin_unlock(&hb->lock); wake_up_q(&wake_q); out_put_key: put_futex_key(&key); @@ -2042,7 +2019,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, struct futex_hash_bucket *hb1, *hb2; struct futex_q *this, *next; DEFINE_WAKE_Q(wake_q); - LIST_HEAD(to_free); if (nr_wake < 0 || nr_requeue < 0) return -EINVAL; @@ -2281,6 +2257,16 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, requeue_pi_wake_futex(this, &key2, hb2); drop_count++; continue; + } else if (ret == -EAGAIN) { + /* + * Waiter was woken by timeout or + * signal and has set pi_blocked_on to + * PI_WAKEUP_INPROGRESS before we + * tried to enqueue it on the rtmutex. + */ + this->pi_state = NULL; + put_pi_state(pi_state); + continue; } else if (ret) { /* * rt_mutex_start_proxy_lock() detected a @@ -2291,7 +2277,7 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, * object. */ this->pi_state = NULL; - put_pi_state_atomic(pi_state, &to_free); + put_pi_state(pi_state); /* * We stop queueing more waiters and let user * space deal with the mess. @@ -2308,7 +2294,7 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We * need to drop it here again. */ - put_pi_state_atomic(pi_state, &to_free); + put_pi_state(pi_state); out_unlock: double_unlock_hb(hb1, hb2); @@ -2329,7 +2315,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, out_put_key1: put_futex_key(&key1); out: - free_pi_state_list(&to_free); return ret ? ret : task_count; } @@ -2353,7 +2338,7 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q) q->lock_ptr = &hb->lock; - raw_spin_lock(&hb->lock); /* implies smp_mb(); (A) */ + spin_lock(&hb->lock); /* implies smp_mb(); (A) */ return hb; } @@ -2361,7 +2346,7 @@ static inline void queue_unlock(struct futex_hash_bucket *hb) __releases(&hb->lock) { - raw_spin_unlock(&hb->lock); + spin_unlock(&hb->lock); hb_waiters_dec(hb); } @@ -2400,7 +2385,7 @@ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) __releases(&hb->lock) { __queue_me(q, hb); - raw_spin_unlock(&hb->lock); + spin_unlock(&hb->lock); } /** @@ -2416,41 +2401,41 @@ static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb) */ static int unqueue_me(struct futex_q *q) { - raw_spinlock_t *lock_ptr; + spinlock_t *lock_ptr; int ret = 0; /* In the common case we don't take the spinlock, which is nice. */ retry: /* - * q->lock_ptr can change between this read and the following - * raw_spin_lock. Use READ_ONCE to forbid the compiler from reloading - * q->lock_ptr and optimizing lock_ptr out of the logic below. + * q->lock_ptr can change between this read and the following spin_lock. + * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and + * optimizing lock_ptr out of the logic below. */ lock_ptr = READ_ONCE(q->lock_ptr); if (lock_ptr != NULL) { - raw_spin_lock(lock_ptr); + spin_lock(lock_ptr); /* * q->lock_ptr can change between reading it and - * raw_spin_lock(), causing us to take the wrong lock. This + * spin_lock(), causing us to take the wrong lock. This * corrects the race condition. * * Reasoning goes like this: if we have the wrong lock, * q->lock_ptr must have changed (maybe several times) - * between reading it and the raw_spin_lock(). It can - * change again after the raw_spin_lock() but only if it was - * already changed before the raw_spin_lock(). It cannot, + * between reading it and the spin_lock(). It can + * change again after the spin_lock() but only if it was + * already changed before the spin_lock(). It cannot, * however, change back to the original value. Therefore * we can detect whether we acquired the correct lock. */ if (unlikely(lock_ptr != q->lock_ptr)) { - raw_spin_unlock(lock_ptr); + spin_unlock(lock_ptr); goto retry; } __unqueue_futex(q); BUG_ON(q->pi_state); - raw_spin_unlock(lock_ptr); + spin_unlock(lock_ptr); ret = 1; } @@ -2466,16 +2451,13 @@ static int unqueue_me(struct futex_q *q) static void unqueue_me_pi(struct futex_q *q) __releases(q->lock_ptr) { - struct futex_pi_state *ps; - __unqueue_futex(q); BUG_ON(!q->pi_state); - ps = __put_pi_state(q->pi_state); + put_pi_state(q->pi_state); q->pi_state = NULL; - raw_spin_unlock(q->lock_ptr); - kfree(ps); + spin_unlock(q->lock_ptr); } static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, @@ -2599,7 +2581,7 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, */ handle_err: raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); - raw_spin_unlock(q->lock_ptr); + spin_unlock(q->lock_ptr); switch (err) { case -EFAULT: @@ -2616,7 +2598,7 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q, break; } - raw_spin_lock(q->lock_ptr); + spin_lock(q->lock_ptr); raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); /* @@ -2730,7 +2712,7 @@ static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q, /* * The task state is guaranteed to be set before another task can * wake it. set_current_state() is implemented using smp_store_mb() and - * queue_me() calls raw_spin_unlock() upon completion, both serializing + * queue_me() calls spin_unlock() upon completion, both serializing * access to the hash list and forcing another memory barrier. */ set_current_state(TASK_INTERRUPTIBLE); @@ -3028,7 +3010,15 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, * before __rt_mutex_start_proxy_lock() is done. */ raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock); - raw_spin_unlock(q.lock_ptr); + /* + * the migrate_disable() here disables migration in the in_atomic() fast + * path which is enabled again in the following spin_unlock(). We have + * one migrate_disable() pending in the slow-path which is reversed + * after the raw_spin_unlock_irq() where we leave the atomic context. + */ + migrate_disable(); + + spin_unlock(q.lock_ptr); /* * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter * such that futex_unlock_pi() is guaranteed to observe the waiter when @@ -3036,6 +3026,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, */ ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current); raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock); + migrate_enable(); if (ret) { if (ret == 1) @@ -3049,7 +3040,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter); cleanup: - raw_spin_lock(q.lock_ptr); + spin_lock(q.lock_ptr); /* * If we failed to acquire the lock (deadlock/signal/timeout), we must * first acquire the hb->lock before removing the lock from the @@ -3136,7 +3127,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) return ret; hb = hash_futex(&key); - raw_spin_lock(&hb->lock); + spin_lock(&hb->lock); /* * Check waiters first. We do not trust user space values at @@ -3170,10 +3161,19 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) * rt_waiter. Also see the WARN in wake_futex_pi(). */ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock); - raw_spin_unlock(&hb->lock); + /* + * Magic trickery for now to make the RT migrate disable + * logic happy. The following spin_unlock() happens with + * interrupts disabled so the internal migrate_enable() + * won't undo the migrate_disable() which was issued when + * locking hb->lock. + */ + migrate_disable(); + spin_unlock(&hb->lock); /* drops pi_state->pi_mutex.wait_lock */ ret = wake_futex_pi(uaddr, uval, pi_state); + migrate_enable(); put_pi_state(pi_state); @@ -3209,7 +3209,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) * owner. */ if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) { - raw_spin_unlock(&hb->lock); + spin_unlock(&hb->lock); switch (ret) { case -EFAULT: goto pi_faulted; @@ -3229,7 +3229,7 @@ static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) ret = (curval == uval) ? 0 : -EAGAIN; out_unlock: - raw_spin_unlock(&hb->lock); + spin_unlock(&hb->lock); out_putkey: put_futex_key(&key); return ret; @@ -3344,7 +3344,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, { struct hrtimer_sleeper timeout, *to = NULL; struct rt_mutex_waiter rt_waiter; - struct futex_hash_bucket *hb; + struct futex_hash_bucket *hb, *hb2; union futex_key key2 = FUTEX_KEY_INIT; struct futex_q q = futex_q_init; int res, ret; @@ -3402,20 +3402,55 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, /* Queue the futex_q, drop the hb lock, wait for wakeup. */ futex_wait_queue_me(hb, &q, to); - raw_spin_lock(&hb->lock); - ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); - raw_spin_unlock(&hb->lock); - if (ret) - goto out_put_keys; + /* + * On RT we must avoid races with requeue and trying to block + * on two mutexes (hb->lock and uaddr2's rtmutex) by + * serializing access to pi_blocked_on with pi_lock. + */ + raw_spin_lock_irq(¤t->pi_lock); + if (current->pi_blocked_on) { + /* + * We have been requeued or are in the process of + * being requeued. + */ + raw_spin_unlock_irq(¤t->pi_lock); + } else { + /* + * Setting pi_blocked_on to PI_WAKEUP_INPROGRESS + * prevents a concurrent requeue from moving us to the + * uaddr2 rtmutex. After that we can safely acquire + * (and possibly block on) hb->lock. + */ + current->pi_blocked_on = PI_WAKEUP_INPROGRESS; + raw_spin_unlock_irq(¤t->pi_lock); + + spin_lock(&hb->lock); + + /* + * Clean up pi_blocked_on. We might leak it otherwise + * when we succeeded with the hb->lock in the fast + * path. + */ + raw_spin_lock_irq(¤t->pi_lock); + current->pi_blocked_on = NULL; + raw_spin_unlock_irq(¤t->pi_lock); + + ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); + spin_unlock(&hb->lock); + if (ret) + goto out_put_keys; + } /* - * In order for us to be here, we know our q.key == key2, and since - * we took the hb->lock above, we also know that futex_requeue() has - * completed and we no longer have to concern ourselves with a wakeup - * race with the atomic proxy lock acquisition by the requeue code. The - * futex_requeue dropped our key1 reference and incremented our key2 - * reference count. + * In order to be here, we have either been requeued, are in + * the process of being requeued, or requeue successfully + * acquired uaddr2 on our behalf. If pi_blocked_on was + * non-null above, we may be racing with a requeue. Do not + * rely on q->lock_ptr to be hb2->lock until after blocking on + * hb->lock or hb2->lock. The futex_requeue dropped our key1 + * reference and incremented our key2 reference count. */ + hb2 = hash_futex(&key2); /* Check if the requeue code acquired the second futex for us. */ if (!q.rt_waiter) { @@ -3424,17 +3459,15 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, * did a lock-steal - fix up the PI-state in that case. */ if (q.pi_state && (q.pi_state->owner != current)) { - struct futex_pi_state *ps_free; - - raw_spin_lock(q.lock_ptr); + spin_lock(&hb2->lock); + BUG_ON(&hb2->lock != q.lock_ptr); ret = fixup_pi_state_owner(uaddr2, &q, current); /* * Drop the reference to the pi state which * the requeue_pi() code acquired for us. */ - ps_free = __put_pi_state(q.pi_state); + put_pi_state(q.pi_state); spin_unlock(&hb2->lock); - kfree(ps_free); /* * Adjust the return value. It's either -EFAULT or * success (1) but the caller expects 0 for success. @@ -3453,7 +3486,8 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, pi_mutex = &q.pi_state->pi_mutex; ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter); - raw_spin_lock(q.lock_ptr); + spin_lock(&hb2->lock); + BUG_ON(&hb2->lock != q.lock_ptr); if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter)) ret = 0; @@ -4212,7 +4246,7 @@ static int __init futex_init(void) for (i = 0; i < futex_hashsize; i++) { atomic_set(&futex_queues[i].waiters, 0); plist_head_init(&futex_queues[i].chain); - raw_spin_lock_init(&futex_queues[i].lock); + spin_lock_init(&futex_queues[i].lock); } return 0; diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 05fcf8a75a51..ded2296f848a 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -142,6 +142,12 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock) WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS); } +static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter) +{ + return waiter && waiter != PI_WAKEUP_INPROGRESS && + waiter != PI_REQUEUE_INPROGRESS; +} + /* * We can speed up the acquire/release, if there's no debugging state to be * set up. @@ -415,7 +421,8 @@ int max_lock_depth = 1024; static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p) { - return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL; + return rt_mutex_real_waiter(p->pi_blocked_on) ? + p->pi_blocked_on->lock : NULL; } /* @@ -551,7 +558,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task, * reached or the state of the chain has changed while we * dropped the locks. */ - if (!waiter) + if (!rt_mutex_real_waiter(waiter)) goto out_unlock_pi; /* @@ -1321,6 +1328,22 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock, return -EDEADLK; raw_spin_lock(&task->pi_lock); + /* + * In the case of futex requeue PI, this will be a proxy + * lock. The task will wake unaware that it is enqueueed on + * this lock. Avoid blocking on two locks and corrupting + * pi_blocked_on via the PI_WAKEUP_INPROGRESS + * flag. futex_wait_requeue_pi() sets this when it wakes up + * before requeue (due to a signal or timeout). Do not enqueue + * the task if PI_WAKEUP_INPROGRESS is set. + */ + if (task != current && task->pi_blocked_on == PI_WAKEUP_INPROGRESS) { + raw_spin_unlock(&task->pi_lock); + return -EAGAIN; + } + + BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)); + waiter->task = task; waiter->lock = lock; waiter->prio = task->prio; @@ -1344,7 +1367,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock, rt_mutex_enqueue_pi(owner, waiter); rt_mutex_adjust_prio(owner); - if (owner->pi_blocked_on) + if (rt_mutex_real_waiter(owner->pi_blocked_on)) chain_walk = 1; } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) { chain_walk = 1; @@ -1444,7 +1467,7 @@ static void remove_waiter(struct rt_mutex *lock, { bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock)); struct task_struct *owner = rt_mutex_owner(lock); - struct rt_mutex *next_lock; + struct rt_mutex *next_lock = NULL; lockdep_assert_held(&lock->wait_lock); @@ -1470,7 +1493,8 @@ static void remove_waiter(struct rt_mutex *lock, rt_mutex_adjust_prio(owner); /* Store the lock on which owner is blocked or NULL */ - next_lock = task_blocked_on_lock(owner); + if (rt_mutex_real_waiter(owner->pi_blocked_on)) + next_lock = task_blocked_on_lock(owner); raw_spin_unlock(&owner->pi_lock); @@ -1506,7 +1530,8 @@ void rt_mutex_adjust_pi(struct task_struct *task) raw_spin_lock_irqsave(&task->pi_lock, flags); waiter = task->pi_blocked_on; - if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) { + if (!rt_mutex_real_waiter(waiter) || + rt_mutex_waiter_equal(waiter, task_to_waiter(task))) { raw_spin_unlock_irqrestore(&task->pi_lock, flags); return; } @@ -2324,6 +2349,34 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock, if (try_to_take_rt_mutex(lock, task, NULL)) return 1; +#ifdef CONFIG_PREEMPT_RT_FULL + /* + * In PREEMPT_RT there's an added race. + * If the task, that we are about to requeue, times out, + * it can set the PI_WAKEUP_INPROGRESS. This tells the requeue + * to skip this task. But right after the task sets + * its pi_blocked_on to PI_WAKEUP_INPROGRESS it can then + * block on the spin_lock(&hb->lock), which in RT is an rtmutex. + * This will replace the PI_WAKEUP_INPROGRESS with the actual + * lock that it blocks on. We *must not* place this task + * on this proxy lock in that case. + * + * To prevent this race, we first take the task's pi_lock + * and check if it has updated its pi_blocked_on. If it has, + * we assume that it woke up and we return -EAGAIN. + * Otherwise, we set the task's pi_blocked_on to + * PI_REQUEUE_INPROGRESS, so that if the task is waking up + * it will know that we are in the process of requeuing it. + */ + raw_spin_lock(&task->pi_lock); + if (task->pi_blocked_on) { + raw_spin_unlock(&task->pi_lock); + return -EAGAIN; + } + task->pi_blocked_on = PI_REQUEUE_INPROGRESS; + raw_spin_unlock(&task->pi_lock); +#endif + /* We enforce deadlock detection for futexes */ ret = task_blocks_on_rt_mutex(lock, waiter, task, RT_MUTEX_FULL_CHAINWALK); diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h index f587e0422d23..8e0c592273e6 100644 --- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -132,6 +132,9 @@ enum rtmutex_chainwalk { /* * PI-futex support (proxy locking functions, etc.): */ +#define PI_WAKEUP_INPROGRESS ((struct rt_mutex_waiter *) 1) +#define PI_REQUEUE_INPROGRESS ((struct rt_mutex_waiter *) 2) + extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock); extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock, struct task_struct *proxy_owner);