This is a note to let you know that I've just added the patch titled
workqueue: fix deadlock in worker_maybe_bind_and_lock()
to the 2.6.38-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
workqueue-fix-deadlock-in-worker_maybe_bind_and_lock.patch
and it can be found in the queue-2.6.38 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 5035b20fa5cd146b66f5f89619c20a4177fb736d Mon Sep 17 00:00:00 2001
From: Tejun Heo <[email protected]>
Date: Fri, 29 Apr 2011 18:08:37 +0200
Subject: workqueue: fix deadlock in worker_maybe_bind_and_lock()
From: Tejun Heo <[email protected]>
commit 5035b20fa5cd146b66f5f89619c20a4177fb736d upstream.
If a rescuer and stop_machine() bringing down a CPU race with each
other, they may deadlock on non-preemptive kernel. The CPU won't
accept a new task, so the rescuer can't migrate to the target CPU,
while stop_machine() can't proceed because the rescuer is holding one
of the CPU retrying migration. GCWQ_DISASSOCIATED is never cleared
and worker_maybe_bind_and_lock() retries indefinitely.
This problem can be reproduced semi reliably while the system is
entering suspend.
http://thread.gmane.org/gmane.linux.kernel/1122051
A lot of kudos to Thilo-Alexander for reporting this tricky issue and
painstaking testing.
stable: This affects all kernels with cmwq, so all kernels since and
including v2.6.36 need this fix.
Signed-off-by: Tejun Heo <[email protected]>
Reported-by: Thilo-Alexander Ginkel <[email protected]>
Tested-by: Thilo-Alexander Ginkel <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
kernel/workqueue.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1283,8 +1283,14 @@ __acquires(&gcwq->lock)
return true;
spin_unlock_irq(&gcwq->lock);
- /* CPU has come up inbetween, retry migration */
+ /*
+ * We've raced with CPU hot[un]plug. Give it a breather
+ * and retry migration. cond_resched() is required here;
+ * otherwise, we might deadlock against cpu_stop trying to
+ * bring down the CPU on non-preemptive kernel.
+ */
cpu_relax();
+ cond_resched();
}
}
Patches currently in stable-queue which might be from [email protected] are
queue-2.6.38/workqueue-fix-deadlock-in-worker_maybe_bind_and_lock.patch
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