path: root/kernel
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authorTejun Heo <tj@kernel.org>2011-04-29 18:08:37 +0200
committerGreg Kroah-Hartman <gregkh@suse.de>2011-05-09 15:06:37 -0700
commit5a19c7ecdc631407d490d206b80ed790daad99cd (patch)
treec1cb59e08e914df903ca5f70ba6264033b62c5b6 /kernel
parentbcd0df39767d1c4352566d909291deac099b222b (diff)
workqueue: fix deadlock in worker_maybe_bind_and_lock()
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 <tj@kernel.org> Reported-by: Thilo-Alexander Ginkel <thilo@ginkel.com> Tested-by: Thilo-Alexander Ginkel <thilo@ginkel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'kernel')
1 files changed, 7 insertions, 1 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index ee6578b578a..7b65ae747c6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1283,8 +1283,14 @@ __acquires(&gcwq->lock)
return true;
- /* 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.
+ */
+ cond_resched();