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Date:	Tue, 7 Oct 2014 09:29:42 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, Joe Lawrence <joe.lawrence@...atus.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] workqueue: add quiescent state between work items

Mon, Oct 06, 2014 at 06:21:58AM CEST, paulmck@...ux.vnet.ibm.com wrote:
>On Sun, Oct 05, 2014 at 03:47:48PM -0400, Tejun Heo wrote:
>> On Sun, Oct 05, 2014 at 03:21:19PM -0400, Tejun Heo wrote:
>> > On Sun, Oct 05, 2014 at 01:24:21PM -0400, Joe Lawrence wrote:
>> > > 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@...atus.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: b22ce2785d97 ("workqueue: cond_resched() after processing each work item")
>> > > Cc: <stable@...r.kernel.org>
>> > 
>> > Applied to wq/for-3.17-fixes.  If 3.17 comes out before this gets
>> > merged, I'll send it as for-3.18.
>> 
>> Oops, the rcu calls aren't in mainline yet.  I think it'd be best to
>> route these through the RCU tree.  Paul, can you please route these
>> two patches?
>> 
>> Acked-by: Tejun Heo <tj@...nel.org>
>
>Will do!
>
>I will try 3.17, failing that, 3.18.


Paul, Tehun, how do you propose to fix this on older kernels which do
not have rcu_note_voluntary_context_switch? I'm particullary interested
in 3.10.

Thanks.
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