From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>
Cc: linux-kernel@vger.kernel.org, Juri Lelli <juri.lelli@redhat.com>,
Waiman Long <longman@redhat.com>
Subject: [PATCH-tip 1/5] locking/ww_mutex: Revert "Treat ww_mutex_lock() like a trylock"
Date: Thu, 18 Mar 2021 13:28:10 -0400 [thread overview]
Message-ID: <20210318172814.4400-2-longman@redhat.com> (raw)
In-Reply-To: <20210318172814.4400-1-longman@redhat.com>
It turns out that treating ww_mutex_lock() as a trylock will fail to catch
real deadlock hazard like:
mutex_lock(&A); ww_mutex_lock(&B, ctx);
ww_mutex_lock(&B, ctx); mutex_lock(&A);
The current lockdep code should be able to handle mixed lock ordering
of ww_mutexes as long as
1) there is a top level nested lock that is acquired before hand, and
2) the nested lock and the ww_mutex are of the same lock class.
Any ww_mutex use cases that do not provide the above guarantee will
have to be modified to avoid lockdep problem.
Revert the previous commit b058f2e4d0a7 ("locking/ww_mutex: Treat
ww_mutex_lock() like a trylock").
Fixes: commit b058f2e4d0a7 ("locking/ww_mutex: Treat ww_mutex_lock() like a trylock")
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/mutex.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index bb89393cd3a2..622ebdfcd083 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -946,10 +946,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
}
preempt_disable();
- /*
- * Treat as trylock for ww_mutex.
- */
- mutex_acquire_nest(&lock->dep_map, subclass, !!ww_ctx, nest_lock, ip);
+ mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
if (__mutex_trylock(lock) ||
mutex_optimistic_spin(lock, ww_ctx, NULL)) {
--
2.18.1
next prev parent reply other threads:[~2021-03-18 17:29 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-18 17:28 [PATCH-tip 0/5] locking/locktorture: Fix locktorture ww_mutex test problems Waiman Long
2021-03-18 17:28 ` Waiman Long [this message]
2021-03-18 17:28 ` [PATCH-tip 2/5] locking/locktorture: Fix false positive circular locking splat in ww_mutex test Waiman Long
2021-03-19 12:54 ` [tip: locking/core] " tip-bot2 for Waiman Long
2021-03-18 17:28 ` [PATCH-tip 3/5] locking/ww_mutex: Remove DEFINE_WW_MUTEX() macro Waiman Long
2021-03-19 12:54 ` [tip: locking/core] " tip-bot2 for Waiman Long
2021-03-18 17:28 ` [PATCH-tip 4/5] locking/locktorture: Pass thread id to lock/unlock functions Waiman Long
2021-03-19 12:54 ` [tip: locking/core] " tip-bot2 for Waiman Long
2021-03-18 17:28 ` [PATCH-tip 5/5] locking/locktorture: locking/locktorture: Fix incorrect use of ww_acquire_ctx in ww_mutex test Waiman Long
2021-03-19 12:54 ` [tip: locking/core] " tip-bot2 for Waiman Long
2021-03-19 11:10 ` [PATCH-tip 0/5] locking/locktorture: Fix locktorture ww_mutex test problems Ingo Molnar
2021-03-19 11:16 ` Ingo Molnar
2021-03-19 15:29 ` Waiman Long
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