The patch below does not apply to the 3.17-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 789cbbeca4eb7141cbd748ee93772471101b507b Mon Sep 17 00:00:00 2001 From: Joe Lawrence <joe.lawrence@xxxxxxxxxxx> Date: Sun, 5 Oct 2014 13:24:21 -0400 Subject: [PATCH] workqueue: Add quiescent state between work items Similar to the stop_machine deadlock scenario on !PREEMPT kernels addressed in b22ce2785d97 "workqueue: cond_resched() after processing each work item", kworker threads requeueing back-to-back with zero jiffy delay can stall RCU. The cond_resched call introduced in that fix will yield only iff there are other higher priority tasks to run, so force a quiescent RCU state between work items. Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxxx> Link: https://lkml.kernel.org/r/20140926105227.01325697@xxxxxxxxxxxxxxxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20140929115445.40221d8e@xxxxxxxxxxxxxxxxxxxxxxxxxxxx Fixes: b22ce2785d97 ("workqueue: cond_resched() after processing each work item") Cc: <stable@xxxxxxxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 5dbe22aa3efd..345bec95e708 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2043,8 +2043,10 @@ __acquires(&pool->lock) * 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. + * stop_machine. At the same time, report a quiescent RCU state so + * the same condition doesn't freeze RCU. */ + rcu_note_voluntary_context_switch(current); cond_resched(); spin_lock_irq(&pool->lock); -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html