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From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 30 Sep 2019 18:15:44 +0200
Subject: [PATCH] locking/rtmutex: Clean ->pi_blocked_on in the error case
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.3-rt1.tar.xz
The function rt_mutex_wait_proxy_lock() cleans ->pi_blocked_on in case
of failure (timeout, signal). The same cleanup is required in
__rt_mutex_start_proxy_lock().
In both the cases the tasks was interrupted by a signal or timeout while
acquiring the lock and after the interruption it longer blocks on the
lock.
Fixes: 1a1fb985f2e2b ("futex: Handle early deadlock return correctly")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/locking/rtmutex.c | 43 +++++++++++++++++++++++++------------------
1 file changed, 25 insertions(+), 18 deletions(-)
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -2137,6 +2137,26 @@ void rt_mutex_proxy_unlock(struct rt_mut
rt_mutex_set_owner(lock, NULL);
}
+static void fixup_rt_mutex_blocked(struct rt_mutex *lock)
+{
+ struct task_struct *tsk = current;
+ /*
+ * RT has a problem here when the wait got interrupted by a timeout
+ * or a signal. task->pi_blocked_on is still set. The task must
+ * acquire the hash bucket lock when returning from this function.
+ *
+ * If the hash bucket lock is contended then the
+ * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
+ * task_blocks_on_rt_mutex() will trigger. This can be avoided by
+ * clearing task->pi_blocked_on which removes the task from the
+ * boosting chain of the rtmutex. That's correct because the task
+ * is not longer blocked on it.
+ */
+ raw_spin_lock(&tsk->pi_lock);
+ tsk->pi_blocked_on = NULL;
+ raw_spin_unlock(&tsk->pi_lock);
+}
+
/**
* __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
* @lock: the rt_mutex to take
@@ -2209,6 +2229,9 @@ int __rt_mutex_start_proxy_lock(struct r
ret = 0;
}
+ if (ret)
+ fixup_rt_mutex_blocked(lock);
+
debug_rt_mutex_print_deadlock(waiter);
return ret;
@@ -2289,7 +2312,6 @@ int rt_mutex_wait_proxy_lock(struct rt_m
struct hrtimer_sleeper *to,
struct rt_mutex_waiter *waiter)
{
- struct task_struct *tsk = current;
int ret;
raw_spin_lock_irq(&lock->wait_lock);
@@ -2301,23 +2323,8 @@ int rt_mutex_wait_proxy_lock(struct rt_m
* have to fix that up.
*/
fixup_rt_mutex_waiters(lock);
- /*
- * RT has a problem here when the wait got interrupted by a timeout
- * or a signal. task->pi_blocked_on is still set. The task must
- * acquire the hash bucket lock when returning from this function.
- *
- * If the hash bucket lock is contended then the
- * BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)) in
- * task_blocks_on_rt_mutex() will trigger. This can be avoided by
- * clearing task->pi_blocked_on which removes the task from the
- * boosting chain of the rtmutex. That's correct because the task
- * is not longer blocked on it.
- */
- if (ret) {
- raw_spin_lock(&tsk->pi_lock);
- tsk->pi_blocked_on = NULL;
- raw_spin_unlock(&tsk->pi_lock);
- }
+ if (ret)
+ fixup_rt_mutex_blocked(lock);
raw_spin_unlock_irq(&lock->wait_lock);
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