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authorTejun Heo <tj@kernel.org>2013-08-28 17:33:37 -0400
committerBen Hutchings <ben@decadent.org.uk>2013-09-10 01:57:36 +0100
commitfbbd6511ab0dff8a79fc5803250b77a1260be354 (patch)
tree50fb3ee9eaf82684875f2d0b2d60718aec0daf34 /kernel
parent8f5f27670088ea31d93287c2bc1e0d54f5ed6841 (diff)
workqueue: cond_resched() after processing each work item
commit b22ce2785d97423846206cceec4efee0c4afd980 upstream. 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 [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/workqueue.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0ad24209221b..0bc9ff0f8e8b 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1920,6 +1920,15 @@ __acquires(&gcwq->lock)
dump_stack();
}
+ /*
+ * The following prevents a kworker from hogging CPU on !PREEMPT
+ * kernels, where a requeueing work item waiting for something to
+ * happen could deadlock with stop_machine as such work item could
+ * indefinitely requeue itself while all other CPUs are trapped in
+ * stop_machine.
+ */
+ cond_resched();
+
spin_lock_irq(&gcwq->lock);
/* clear cpu intensive status */