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workqueue: Add quiescent state between work items 

Similar to the stop_machine deadlock scenario on !PREEMPT kernels
addressed in b22ce2785d "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@stratus.com>
Link: https://lkml.kernel.org/r/20140926105227.01325697@jlaw-desktop.mno.stratus.com
Link: https://lkml.kernel.org/r/20140929115445.40221d8e@jlaw-desktop.mno.stratus.com
Fixes: b22ce2785d ("workqueue: cond_resched() after processing each work item")
Cc: <stable@vger.kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Joe Lawrence 2014-10-05 13:24:21 -04:00 committed by Paul E. McKenney
parent c98fed9fc6
commit 789cbbeca4
1 changed files with 3 additions and 1 deletions
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4
kernel/workqueue.c
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@ -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);