From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Lai Jiangshan <laijs@cn.fujitsu.com>
Subject: [patch 1/6] rtmutex: Fix deadlock detector for real
Date: Thu, 22 May 2014 03:25:39 -0000 [thread overview]
Message-ID: <20140522031949.725272460@linutronix.de> (raw)
In-Reply-To: 20140522031841.797415507@linutronix.de
[-- Attachment #1: rtmutex-fix-deadlock-detector-for-real.patch --]
[-- Type: text/plain, Size: 2662 bytes --]
The current deadlock detection logic does not work reliably due to the
following early exit path:
/*
* Drop out, when the task has no waiters. Note,
* top_waiter can be NULL, when we are in the deboosting
* mode!
*/
if (top_waiter && (!task_has_pi_waiters(task) ||
top_waiter != task_top_pi_waiter(task)))
goto out_unlock_pi;
So this not only exits when the task has no waiters, it also exits
unconditionally when the current waiter is not the top priority waiter
of the task.
So in a nested locking scenario, it might abort the lock chain walk
and therefor miss a potential deadlock.
Simple fix: Continue the chain walk, when deadlock detection is
enabled.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
---
kernel/locking/rtmutex.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
Index: tip/kernel/locking/rtmutex.c
===================================================================
--- tip.orig/kernel/locking/rtmutex.c
+++ tip/kernel/locking/rtmutex.c
@@ -343,16 +343,22 @@ static int rt_mutex_adjust_prio_chain(st
* top_waiter can be NULL, when we are in the deboosting
* mode!
*/
- if (top_waiter && (!task_has_pi_waiters(task) ||
- top_waiter != task_top_pi_waiter(task)))
- goto out_unlock_pi;
+ if (top_waiter) {
+ if (!task_has_pi_waiters(task))
+ goto out_unlock_pi;
+
+ if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
+ goto out_unlock_pi;
+ }
/*
* When deadlock detection is off then we check, if further
* priority adjustment is necessary.
*/
- if (!detect_deadlock && waiter->prio == task->prio)
- goto out_unlock_pi;
+ if (waiter->prio == task->prio) {
+ if (!detect_deadlock)
+ goto out_unlock_pi;
+ }
lock = waiter->lock;
if (!raw_spin_trylock(&lock->wait_lock)) {
@@ -361,7 +367,12 @@ static int rt_mutex_adjust_prio_chain(st
goto retry;
}
- /* Deadlock detection */
+ /*
+ * Deadlock detection. If the lock is the same as the original
+ * lock which caused us to walk the lock chain or if the
+ * current lock is owned by the task which initiated the chain
+ * walk, we detected a deadlock.
+ */
if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
raw_spin_unlock(&lock->wait_lock);
@@ -527,6 +538,10 @@ static int task_blocks_on_rt_mutex(struc
unsigned long flags;
int chain_walk = 0, res;
+ /* Early deadlock detection */
+ if (detect_deadlock && owner == task)
+ return -EDEADLK;
+
raw_spin_lock_irqsave(&task->pi_lock, flags);
__rt_mutex_adjust_prio(task);
waiter->task = task;
next prev parent reply other threads:[~2014-05-22 3:25 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-22 3:25 [patch 0/6] rtmutex: Repair deadlock detector and cleanup Thomas Gleixner
2014-05-22 3:25 ` Thomas Gleixner [this message]
2014-05-27 22:09 ` [patch 1/6] rtmutex: Fix deadlock detector for real Steven Rostedt
2014-05-28 9:57 ` Thomas Gleixner
2014-05-28 19:28 ` [tip:core/urgent] " tip-bot for Thomas Gleixner
2014-05-22 3:25 ` [patch 2/6] rtmutex: Remove builtin tester Thomas Gleixner
2014-05-30 21:36 ` Steven Rostedt
2014-05-22 3:25 ` [patch 3/6] rtmutex: Cleanup deadlock detector debug logic Thomas Gleixner
2014-05-30 22:08 ` Steven Rostedt
2014-06-21 20:32 ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-05-22 3:25 ` [patch 4/6] rtmutex: Confine deadlock logic to futex Thomas Gleixner
2014-05-22 7:10 ` Peter Zijlstra
2014-05-28 20:28 ` Thomas Gleixner
2014-05-31 2:06 ` Steven Rostedt
2014-05-22 3:25 ` [patch 5/6] rtmutex: Clarify the lock chain walk Thomas Gleixner
2014-05-31 2:19 ` Steven Rostedt
2014-05-22 3:25 ` [patch 6/6] rtmutex: Avoid pointless requeueing in the deadlock detection " Thomas Gleixner
2014-05-27 22:49 ` Jason Low
2014-05-28 9:43 ` Thomas Gleixner
2014-05-31 2:21 ` Steven Rostedt
2014-06-21 20:33 ` [tip:locking/core] " tip-bot for Thomas Gleixner
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