From: tip-bot for Prateek Sood <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: prsood@codeaurora.org, mingo@kernel.org,
linux-kernel@vger.kernel.org, dbueso@suse.de,
torvalds@linux-foundation.org, tglx@linutronix.de,
andrea.parri@amarulasolutions.com, hpa@zytor.com,
peterz@infradead.org
Subject: [tip:locking/core] sched/wait: Fix rcuwait_wake_up() ordering
Date: Mon, 21 Jan 2019 03:25:44 -0800 [thread overview]
Message-ID: <tip-6dc080eeb2ba01973bfff0d79844d7a59e12542e@git.kernel.org> (raw)
In-Reply-To: <1543590656-7157-1-git-send-email-prsood@codeaurora.org>
Commit-ID: 6dc080eeb2ba01973bfff0d79844d7a59e12542e
Gitweb: https://git.kernel.org/tip/6dc080eeb2ba01973bfff0d79844d7a59e12542e
Author: Prateek Sood <prsood@codeaurora.org>
AuthorDate: Fri, 30 Nov 2018 20:40:56 +0530
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 21 Jan 2019 11:15:36 +0100
sched/wait: Fix rcuwait_wake_up() ordering
For some peculiar reason rcuwait_wake_up() has the right barrier in
the comment, but not in the code.
This mistake has been observed to cause a deadlock in the following
situation:
P1 P2
percpu_up_read() percpu_down_write()
rcu_sync_is_idle() // false
rcu_sync_enter()
...
__percpu_up_read()
[S] ,- __this_cpu_dec(*sem->read_count)
| smp_rmb();
[L] | task = rcu_dereference(w->task) // NULL
|
| [S] w->task = current
| smp_mb();
| [L] readers_active_check() // fail
`-> <store happens here>
Where the smp_rmb() (obviously) fails to constrain the store.
[ peterz: Added changelog. ]
Signed-off-by: Prateek Sood <prsood@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 8f95c90ceb54 ("sched/wait, RCU: Introduce rcuwait machinery")
Link: https://lkml.kernel.org/r/1543590656-7157-1-git-send-email-prsood@codeaurora.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/exit.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 284f2fe9a293..3fb7be001964 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -307,7 +307,7 @@ void rcuwait_wake_up(struct rcuwait *w)
* MB (A) MB (B)
* [L] cond [L] tsk
*/
- smp_rmb(); /* (B) */
+ smp_mb(); /* (B) */
/*
* Avoid using task_rcu_dereference() magic as long as we are careful,
prev parent reply other threads:[~2019-01-21 11:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-30 15:10 [PATCH] percpu_rwsem: fix missed wakeup due to reordering of load Prateek Sood
2018-12-03 6:38 ` Davidlohr Bueso
2018-12-03 19:36 ` Prateek Sood
2018-12-12 14:26 ` Prateek Sood
2018-12-12 15:31 ` Davidlohr Bueso
2018-12-21 7:29 ` Prateek Sood
2018-12-21 9:45 ` Andrea Parri
2018-12-12 15:28 ` Andrea Parri
2018-12-21 6:35 ` Prateek Sood
2019-01-21 11:25 ` tip-bot for Prateek Sood [this message]
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