| From 19491de1201af8b1a506b32387a875dfb3bec2f9 Mon Sep 17 00:00:00 2001 |
| From: Darren Hart <dvhltc@us.ibm.com> |
| Date: Fri, 9 Jul 2010 17:50:23 -0400 |
| Subject: [PATCH] futex: Protect against pi_blocked_on corruption during requeue PI |
| |
| commit 19491de1201af8b1a506b32387a875dfb3bec2f9 in tip. |
| |
| The requeue_pi mechanism introduced proxy locking of the rtmutex. This |
| creates a scenario where a task can wakeup, not knowing it has been |
| enqueued on an rtmutex. Blocking on an hb->lock() can overwrite a |
| valid value in current->pi_blocked_on, leading to an inconsistent |
| state. |
| |
| Prevent overwriting pi_blocked_on by serializing on the waiter's |
| pi_lock and using the new PI_WAKEUP_INPROGRESS state flag to indicate |
| a waiter that has been woken by a timeout or signal. This prevents the |
| rtmutex code from adding the waiter to the rtmutex wait list, |
| returning EAGAIN to futex_requeue(), which will in turn ignore the |
| waiter during a requeue. Care is taken to allow current to block on |
| locks even if PI_WAKEUP_INPROGRESS is set. |
| |
| During normal wakeup, this results in one less hb->lock protected |
| section. In the pre-requeue-timeout-or-signal wakeup, this removes the |
| "greedy locking" behavior, no attempt will be made to acquire the |
| lock. |
| |
| [ tglx: take pi_lock with lock_irq(), removed paranoid warning, |
| plugged pi_state and pi_blocked_on leak, adjusted some |
| comments ] |
| |
| Signed-off-by: Darren Hart <dvhltc@us.ibm.com> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Eric Dumazet <eric.dumazet@gmail.com> |
| Cc: John Kacur <jkacur@redhat.com> |
| Cc: Steven Rostedt <rostedt@goodmis.org> |
| Cc: Mike Galbraith <efault@gmx.de> |
| LKML-Reference: <4C3C1DCF.9090509@us.ibm.com> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| |
| diff --git a/kernel/futex.c b/kernel/futex.c |
| index e7a35f1..6085332 100644 |
| --- a/kernel/futex.c |
| +++ b/kernel/futex.c |
| @@ -1334,6 +1334,16 @@ retry_private: |
| 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; |
| + free_pi_state(pi_state); |
| + continue; |
| } else if (ret) { |
| /* -EDEADLK */ |
| this->pi_state = NULL; |
| @@ -2209,9 +2219,9 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared, |
| int clockrt, u32 __user *uaddr2) |
| { |
| struct hrtimer_sleeper timeout, *to = NULL; |
| + struct futex_hash_bucket *hb, *hb2; |
| struct rt_mutex_waiter rt_waiter; |
| struct rt_mutex *pi_mutex = NULL; |
| - struct futex_hash_bucket *hb; |
| union futex_key key2; |
| struct futex_q q; |
| int res, ret; |
| @@ -2253,18 +2263,54 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared, |
| /* 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_put_keys; |
| + /* |
| + * 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 acquition by the requeue code. |
| + * 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. |
| */ |
| + hb2 = hash_futex(&key2); |
| |
| /* Check if the requeue code acquired the second futex for us. */ |
| if (!q.rt_waiter) { |
| @@ -2273,10 +2319,12 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared, |
| * 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, |
| fshared); |
| - spin_unlock(q.lock_ptr); |
| + spin_unlock(&hb2->lock); |
| } |
| } else { |
| /* |
| @@ -2289,7 +2337,9 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared, |
| ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1); |
| debug_rt_mutex_free_waiter(&rt_waiter); |
| |
| - spin_lock(q.lock_ptr); |
| + spin_lock(&hb2->lock); |
| + BUG_ON(&hb2->lock != q.lock_ptr); |
| + |
| /* |
| * Fixup the pi_state owner and possibly acquire the lock if we |
| * haven't already. |
| diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c |
| index 23dd443..348b1e7 100644 |
| --- a/kernel/rtmutex.c |
| +++ b/kernel/rtmutex.c |
| @@ -82,6 +82,11 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock) |
| clear_rt_mutex_waiters(lock); |
| } |
| |
| +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 the architecture |
| * supports cmpxchg and if there's no debugging state to be set up |
| @@ -227,7 +232,7 @@ 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 || !waiter->task) |
| + if (!rt_mutex_real_waiter(waiter) || !waiter->task) |
| goto out_unlock_pi; |
| |
| /* |
| @@ -448,6 +453,23 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock, |
| int chain_walk = 0, res; |
| |
| 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)); |
| + |
| __rt_mutex_adjust_prio(task); |
| waiter->task = task; |
| waiter->lock = lock; |
| @@ -469,7 +491,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock, |
| plist_add(&waiter->pi_list_entry, &owner->pi_waiters); |
| |
| __rt_mutex_adjust_prio(owner); |
| - if (owner->pi_blocked_on) |
| + if (rt_mutex_real_waiter(owner->pi_blocked_on)) |
| chain_walk = 1; |
| raw_spin_unlock(&owner->pi_lock); |
| } |
| @@ -624,7 +646,7 @@ static void remove_waiter(struct rt_mutex *lock, |
| } |
| __rt_mutex_adjust_prio(owner); |
| |
| - if (owner->pi_blocked_on) |
| + if (rt_mutex_real_waiter(owner->pi_blocked_on)) |
| chain_walk = 1; |
| |
| raw_spin_unlock(&owner->pi_lock); |
| @@ -658,7 +680,8 @@ void rt_mutex_adjust_pi(struct task_struct *task) |
| raw_spin_lock_irqsave(&task->pi_lock, flags); |
| |
| waiter = task->pi_blocked_on; |
| - if (!waiter || waiter->list_entry.prio == task->prio) { |
| + if (!rt_mutex_real_waiter(waiter) || |
| + waiter->list_entry.prio == task->prio) { |
| raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| return; |
| } |
| @@ -1527,7 +1550,7 @@ int rt_mutex_start_proxy_lock(struct rt_mutex *lock, |
| ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock, |
| flags); |
| |
| - if (ret && !waiter->task) { |
| + if (ret == -EDEADLK && !waiter->task) { |
| /* |
| * Reset the return value. We might have |
| * returned with -EDEADLK and the owner |
| diff --git a/kernel/rtmutex_common.h b/kernel/rtmutex_common.h |
| index 4df690c..97fc68c 100644 |
| --- a/kernel/rtmutex_common.h |
| +++ b/kernel/rtmutex_common.h |
| @@ -115,6 +115,9 @@ static inline unsigned long rt_mutex_owner_pending(struct rt_mutex *lock) |
| /* |
| * 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); |
| -- |
| 1.7.1.1 |
| |