]> git.karo-electronics.de Git - linux-beck.git/commit
workqueue: cond_resched() after processing each work item
authorTejun Heo <tj@kernel.org>
Wed, 28 Aug 2013 21:33:37 +0000 (17:33 -0400)
committerTejun Heo <tj@kernel.org>
Thu, 29 Aug 2013 13:19:28 +0000 (09:19 -0400)
commitb22ce2785d97423846206cceec4efee0c4afd980
treeb58beb6df891299ca0d827979c32042ce7969cc4
parentc95389b4cd6a4b52af78bea706a274453e886251
workqueue: cond_resched() after processing each work item

If !PREEMPT, a kworker running work items back to back can hog CPU.
This becomes dangerous when a self-requeueing work item which is
waiting for something to happen races against stop_machine.  Such
self-requeueing work item would requeue itself indefinitely hogging
the kworker and CPU it's running on while stop_machine would wait for
that CPU to enter stop_machine while preventing anything else from
happening on all other CPUs.  The two would deadlock.

Jamie Liu reports that this deadlock scenario exists around
scsi_requeue_run_queue() and libata port multiplier support, where one
port may exclude command processing from other ports.  With the right
timing, scsi_requeue_run_queue() can end up requeueing itself trying
to execute an IO which is asked to be retried while another device has
an exclusive access, which in turn can't make forward progress due to
stop_machine.

Fix it by invoking cond_resched() after executing each work item.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Jamie Liu <jamieliu@google.com>
References: http://thread.gmane.org/gmane.linux.kernel/1552567
Cc: stable@vger.kernel.org
--
 kernel/workqueue.c |    9 +++++++++
 1 file changed, 9 insertions(+)
kernel/workqueue.c