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.lawre...@stratus.com> Link: https://lkml.kernel.org/r/20140926105227.01325...@jlaw-desktop.mno.stratus.com Link: https://lkml.kernel.org/r/20140929115445.40221...@jlaw-desktop.mno.stratus.com Fixes: b22ce2785d97 ("workqueue: cond_resched() after processing each work item") Cc: <sta...@vger.kernel.org> --- kernel/workqueue.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 5dbe22a..345bec9 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); -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
