262 lines
9.2 KiB
Diff
262 lines
9.2 KiB
Diff
From 52fc3041fc0bb78f7ef6ba817fc1221e201ae18b Mon Sep 17 00:00:00 2001
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Message-Id: <52fc3041fc0bb78f7ef6ba817fc1221e201ae18b.1594742966.git.zanussi@kernel.org>
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In-Reply-To: <832f7d97d6b989a5b4860dd2dbec58ad6ad5ab81.1594742966.git.zanussi@kernel.org>
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References: <832f7d97d6b989a5b4860dd2dbec58ad6ad5ab81.1594742966.git.zanussi@kernel.org>
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Wed, 26 Jun 2019 17:44:21 +0200
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Subject: [PATCH 274/329] Revert "rtmutex: Handle the various new futex race
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conditions"
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.132-rt59.tar.xz
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[ Upstream commit 9e0265c21af4d6388d47dcd5ce20f76ec3a2e468 ]
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Drop the RT fixup, the futex code will be changed to avoid the need for
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the workaround.
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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---
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kernel/futex.c | 77 +++++++--------------------------
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kernel/locking/rtmutex.c | 36 +++------------
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kernel/locking/rtmutex_common.h | 2 -
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3 files changed, 21 insertions(+), 94 deletions(-)
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diff --git a/kernel/futex.c b/kernel/futex.c
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index b99266393c52..1f9dd186b00c 100644
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--- a/kernel/futex.c
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+++ b/kernel/futex.c
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@@ -2167,16 +2167,6 @@ 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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@@ -3255,7 +3245,7 @@ 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, *hb2;
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+ struct futex_hash_bucket *hb;
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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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@@ -3313,55 +3303,20 @@ 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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- /*
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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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+ 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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- * 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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+ * 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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*/
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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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@@ -3370,8 +3325,7 @@ 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(&hb2->lock);
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- BUG_ON(&hb2->lock != q.lock_ptr);
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+ spin_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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@@ -3382,7 +3336,7 @@ 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(&hb2->lock);
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+ spin_unlock(q.lock_ptr);
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}
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} else {
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struct rt_mutex *pi_mutex;
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@@ -3396,8 +3350,7 @@ 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(&hb2->lock);
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- BUG_ON(&hb2->lock != q.lock_ptr);
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+ spin_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 7f6f402e04ae..44a33057a83a 100644
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--- a/kernel/locking/rtmutex.c
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+++ b/kernel/locking/rtmutex.c
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@@ -142,11 +142,6 @@ 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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@@ -420,8 +415,7 @@ 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 rt_mutex_real_waiter(p->pi_blocked_on) ?
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- p->pi_blocked_on->lock : NULL;
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+ return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
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}
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/*
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@@ -557,7 +551,7 @@ 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 (!rt_mutex_real_waiter(waiter))
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+ if (!waiter)
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goto out_unlock_pi;
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/*
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@@ -1327,22 +1321,6 @@ 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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- * 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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waiter->task = task;
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waiter->lock = lock;
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waiter->prio = task->prio;
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@@ -1366,7 +1344,7 @@ 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 (rt_mutex_real_waiter(owner->pi_blocked_on))
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+ if (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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@@ -1466,7 +1444,7 @@ 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 = NULL;
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+ struct rt_mutex *next_lock;
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lockdep_assert_held(&lock->wait_lock);
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@@ -1492,8 +1470,7 @@ 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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- if (rt_mutex_real_waiter(owner->pi_blocked_on))
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- next_lock = task_blocked_on_lock(owner);
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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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@@ -1529,8 +1506,7 @@ 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 (!rt_mutex_real_waiter(waiter) ||
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- rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
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+ if (!waiter || 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 a501f3b47081..758dc43872e5 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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@@ -132,8 +132,6 @@ 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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2.17.1
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