diff options
Diffstat (limited to 'features/rt/locking-rtmutex-Handle-the-various-new-futex-race-co.patch')
| -rw-r--r-- | features/rt/locking-rtmutex-Handle-the-various-new-futex-race-co.patch | 255 |
1 files changed, 255 insertions, 0 deletions
diff --git a/features/rt/locking-rtmutex-Handle-the-various-new-futex-race-co.patch b/features/rt/locking-rtmutex-Handle-the-various-new-futex-race-co.patch new file mode 100644 index 00000000..12a83eab --- /dev/null +++ b/features/rt/locking-rtmutex-Handle-the-various-new-futex-race-co.patch @@ -0,0 +1,255 @@ +From d8b0c4e14162b18ee6a955f443a6a1b3fa8473e1 Mon Sep 17 00:00:00 2001 +From: Thomas Gleixner <tglx@linutronix.de> +Date: Fri, 10 Jun 2011 11:04:15 +0200 +Subject: [PATCH 065/191] locking/rtmutex: Handle the various new futex race + conditions + +RT opens a few new interesting race conditions in the rtmutex/futex +combo due to futex hash bucket lock being a 'sleeping' spinlock and +therefor not disabling preemption. + +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +--- + kernel/futex.c | 78 ++++++++++++++++++++++++++------- + kernel/locking/rtmutex.c | 36 ++++++++++++--- + kernel/locking/rtmutex_common.h | 2 + + 3 files changed, 95 insertions(+), 21 deletions(-) + +diff --git a/kernel/futex.c b/kernel/futex.c +index e68db7745039..0315333c0587 100644 +--- a/kernel/futex.c ++++ b/kernel/futex.c +@@ -2154,6 +2154,16 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags, + */ + requeue_pi_wake_futex(this, &key2, hb2); + 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 +@@ -3171,7 +3181,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, + { + struct hrtimer_sleeper timeout, *to; + 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; +@@ -3223,20 +3233,55 @@ 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); + +- spin_lock(&hb->lock); +- ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to); +- spin_unlock(&hb->lock); +- if (ret) +- goto out; ++ /* ++ * 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; ++ } + + /* +- * 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) { +@@ -3245,14 +3290,16 @@ 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)) { +- 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. + */ + put_pi_state(q.pi_state); +- spin_unlock(q.lock_ptr); ++ spin_unlock(&hb2->lock); ++ + /* + * Adjust the return value. It's either -EFAULT or + * success (1) but the caller expects 0 for success. +@@ -3271,7 +3318,8 @@ 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); + +- 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; + +diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c +index c9a37b6d6ea0..7fff3b88b96b 100644 +--- a/kernel/locking/rtmutex.c ++++ b/kernel/locking/rtmutex.c +@@ -136,6 +136,11 @@ 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; ++} ++ + /* + * We can speed up the acquire/release, if there's no debugging state to be + * set up. +@@ -360,7 +365,8 @@ 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; + } + + /* +@@ -496,7 +502,7 @@ 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; + + /* +@@ -929,6 +935,22 @@ 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; +@@ -952,7 +974,7 @@ 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; +@@ -1048,7 +1070,7 @@ 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); + +@@ -1074,7 +1096,8 @@ 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); + +@@ -1110,7 +1133,8 @@ 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; + } +diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h +index b1455dc2366f..096b16cfb096 100644 +--- a/kernel/locking/rtmutex_common.h ++++ b/kernel/locking/rtmutex_common.h +@@ -125,6 +125,8 @@ enum rtmutex_chainwalk { + /* + * PI-futex support (proxy locking functions, etc.): + */ ++#define PI_WAKEUP_INPROGRESS ((struct rt_mutex_waiter *) 1) ++ + 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); +-- +2.19.1 + |