forked from rrcarlosr/Jetpack
256 lines
8.8 KiB
Diff
256 lines
8.8 KiB
Diff
From af50b8149e9e8a4b538d7796a470d4b71121d58d Mon Sep 17 00:00:00 2001
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Fri, 10 Jun 2011 11:04:15 +0200
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Subject: [PATCH 166/352] rtmutex: Handle the various new futex race conditions
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RT opens a few new interesting race conditions in the rtmutex/futex
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combo due to futex hash bucket lock being a 'sleeping' spinlock and
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therefor not disabling preemption.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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---
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kernel/futex.c | 77 +++++++++++++++++++++++++++++++++--------
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kernel/locking/rtmutex.c | 37 ++++++++++++++++----
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kernel/locking/rtmutex_common.h | 2 ++
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3 files changed, 95 insertions(+), 21 deletions(-)
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diff --git a/kernel/futex.c b/kernel/futex.c
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index 7431ff3..601490b 100644
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--- a/kernel/futex.c
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+++ b/kernel/futex.c
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@@ -2062,6 +2062,16 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
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requeue_pi_wake_futex(this, &key2, hb2);
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drop_count++;
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continue;
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+ } else if (ret == -EAGAIN) {
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+ /*
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+ * Waiter was woken by timeout or
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+ * signal and has set pi_blocked_on to
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+ * PI_WAKEUP_INPROGRESS before we
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+ * tried to enqueue it on the rtmutex.
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+ */
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+ this->pi_state = NULL;
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+ put_pi_state(pi_state);
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+ continue;
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} else if (ret) {
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/*
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* rt_mutex_start_proxy_lock() detected a
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@@ -3047,7 +3057,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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struct hrtimer_sleeper timeout, *to = NULL;
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struct futex_pi_state *pi_state = NULL;
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struct rt_mutex_waiter rt_waiter;
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- struct futex_hash_bucket *hb;
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+ struct futex_hash_bucket *hb, *hb2;
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union futex_key key2 = FUTEX_KEY_INIT;
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struct futex_q q = futex_q_init;
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int res, ret;
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@@ -3103,20 +3113,55 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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/* Queue the futex_q, drop the hb lock, wait for wakeup. */
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futex_wait_queue_me(hb, &q, to);
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- spin_lock(&hb->lock);
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- ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
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- spin_unlock(&hb->lock);
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- if (ret)
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- goto out_put_keys;
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+ /*
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+ * On RT we must avoid races with requeue and trying to block
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+ * on two mutexes (hb->lock and uaddr2's rtmutex) by
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+ * serializing access to pi_blocked_on with pi_lock.
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+ */
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+ raw_spin_lock_irq(¤t->pi_lock);
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+ if (current->pi_blocked_on) {
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+ /*
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+ * We have been requeued or are in the process of
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+ * being requeued.
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+ */
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+ raw_spin_unlock_irq(¤t->pi_lock);
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+ } else {
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+ /*
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+ * Setting pi_blocked_on to PI_WAKEUP_INPROGRESS
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+ * prevents a concurrent requeue from moving us to the
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+ * uaddr2 rtmutex. After that we can safely acquire
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+ * (and possibly block on) hb->lock.
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+ */
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+ current->pi_blocked_on = PI_WAKEUP_INPROGRESS;
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+ raw_spin_unlock_irq(¤t->pi_lock);
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+
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+ spin_lock(&hb->lock);
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+
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+ /*
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+ * Clean up pi_blocked_on. We might leak it otherwise
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+ * when we succeeded with the hb->lock in the fast
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+ * path.
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+ */
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+ raw_spin_lock_irq(¤t->pi_lock);
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+ current->pi_blocked_on = NULL;
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+ raw_spin_unlock_irq(¤t->pi_lock);
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+
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+ ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
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+ spin_unlock(&hb->lock);
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+ if (ret)
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+ goto out_put_keys;
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+ }
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/*
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- * In order for us to be here, we know our q.key == key2, and since
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- * we took the hb->lock above, we also know that futex_requeue() has
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- * completed and we no longer have to concern ourselves with a wakeup
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- * race with the atomic proxy lock acquisition by the requeue code. The
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- * futex_requeue dropped our key1 reference and incremented our key2
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- * reference count.
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+ * In order to be here, we have either been requeued, are in
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+ * the process of being requeued, or requeue successfully
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+ * acquired uaddr2 on our behalf. If pi_blocked_on was
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+ * non-null above, we may be racing with a requeue. Do not
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+ * rely on q->lock_ptr to be hb2->lock until after blocking on
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+ * hb->lock or hb2->lock. The futex_requeue dropped our key1
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+ * reference and incremented our key2 reference count.
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*/
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+ hb2 = hash_futex(&key2);
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/* Check if the requeue code acquired the second futex for us. */
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if (!q.rt_waiter) {
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@@ -3125,7 +3170,8 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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* did a lock-steal - fix up the PI-state in that case.
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*/
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if (q.pi_state && (q.pi_state->owner != current)) {
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- spin_lock(q.lock_ptr);
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+ spin_lock(&hb2->lock);
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+ BUG_ON(&hb2->lock != q.lock_ptr);
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ret = fixup_pi_state_owner(uaddr2, &q, current);
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if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
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pi_state = q.pi_state;
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@@ -3136,7 +3182,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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* the requeue_pi() code acquired for us.
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*/
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put_pi_state(q.pi_state);
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- spin_unlock(q.lock_ptr);
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+ spin_unlock(&hb2->lock);
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}
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} else {
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struct rt_mutex *pi_mutex;
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@@ -3150,7 +3196,8 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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pi_mutex = &q.pi_state->pi_mutex;
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ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
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- spin_lock(q.lock_ptr);
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+ spin_lock(&hb2->lock);
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+ BUG_ON(&hb2->lock != q.lock_ptr);
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if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
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ret = 0;
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diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
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index 4b6fdcd8..f7c0478 100644
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--- a/kernel/locking/rtmutex.c
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+++ b/kernel/locking/rtmutex.c
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@@ -133,6 +133,11 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
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WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
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}
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+static int rt_mutex_real_waiter(struct rt_mutex_waiter *waiter)
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+{
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+ return waiter && waiter != PI_WAKEUP_INPROGRESS;
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+}
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+
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/*
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* We can speed up the acquire/release, if there's no debugging state to be
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* set up.
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@@ -389,7 +394,8 @@ int max_lock_depth = 1024;
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static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
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{
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- return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
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+ return rt_mutex_real_waiter(p->pi_blocked_on) ?
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+ p->pi_blocked_on->lock : NULL;
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}
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/*
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@@ -525,7 +531,7 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
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* reached or the state of the chain has changed while we
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* dropped the locks.
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*/
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- if (!waiter)
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+ if (!rt_mutex_real_waiter(waiter))
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goto out_unlock_pi;
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/*
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@@ -961,6 +967,23 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
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return -EDEADLK;
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raw_spin_lock(&task->pi_lock);
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+
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+ /*
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+ * In the case of futex requeue PI, this will be a proxy
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+ * lock. The task will wake unaware that it is enqueueed on
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+ * this lock. Avoid blocking on two locks and corrupting
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+ * pi_blocked_on via the PI_WAKEUP_INPROGRESS
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+ * flag. futex_wait_requeue_pi() sets this when it wakes up
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+ * before requeue (due to a signal or timeout). Do not enqueue
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+ * the task if PI_WAKEUP_INPROGRESS is set.
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+ */
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+ if (task != current && task->pi_blocked_on == PI_WAKEUP_INPROGRESS) {
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+ raw_spin_unlock(&task->pi_lock);
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+ return -EAGAIN;
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+ }
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+
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+ BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on));
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+
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rt_mutex_adjust_prio(task);
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waiter->task = task;
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waiter->lock = lock;
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@@ -985,7 +1008,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
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rt_mutex_enqueue_pi(owner, waiter);
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rt_mutex_adjust_prio(owner);
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- if (owner->pi_blocked_on)
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+ if (rt_mutex_real_waiter(owner->pi_blocked_on))
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chain_walk = 1;
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} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
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chain_walk = 1;
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@@ -1081,7 +1104,7 @@ static void remove_waiter(struct rt_mutex *lock,
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{
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bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
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struct task_struct *owner = rt_mutex_owner(lock);
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- struct rt_mutex *next_lock;
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+ struct rt_mutex *next_lock = NULL;
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lockdep_assert_held(&lock->wait_lock);
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@@ -1107,7 +1130,8 @@ static void remove_waiter(struct rt_mutex *lock,
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rt_mutex_adjust_prio(owner);
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/* Store the lock on which owner is blocked or NULL */
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- next_lock = task_blocked_on_lock(owner);
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+ if (rt_mutex_real_waiter(owner->pi_blocked_on))
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+ next_lock = task_blocked_on_lock(owner);
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raw_spin_unlock(&owner->pi_lock);
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@@ -1143,7 +1167,8 @@ void rt_mutex_adjust_pi(struct task_struct *task)
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raw_spin_lock_irqsave(&task->pi_lock, flags);
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waiter = task->pi_blocked_on;
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- if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
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+ if (!rt_mutex_real_waiter(waiter) ||
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+ rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
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raw_spin_unlock_irqrestore(&task->pi_lock, flags);
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return;
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}
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diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
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index 722e3cf..be1c017 100644
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--- a/kernel/locking/rtmutex_common.h
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+++ b/kernel/locking/rtmutex_common.h
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@@ -99,6 +99,8 @@ enum rtmutex_chainwalk {
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/*
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* PI-futex support (proxy locking functions, etc.):
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*/
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+#define PI_WAKEUP_INPROGRESS ((struct rt_mutex_waiter *) 1)
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+
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extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);
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extern void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
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struct task_struct *proxy_owner);
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--
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2.7.4
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