workqueue: fix deadlock in worker_maybe_bind_and_lock()
authorTejun Heo <tj@kernel.org>
Fri, 29 Apr 2011 16:08:37 +0000 (18:08 +0200)
committerTejun Heo <tj@kernel.org>
Fri, 29 Apr 2011 16:08:37 +0000 (18:08 +0200)
commit5035b20fa5cd146b66f5f89619c20a4177fb736d
treecd62bba3a3c36164d0faaac1b3c922be0eca11f1
parente2de9e0862778f4aba103027ce575efbddb8117f
workqueue: fix deadlock in worker_maybe_bind_and_lock()

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>
Cc: stable@kernel.org
kernel/workqueue.c