linux-kernel - Re: [PATCH v2 1/2] workqueue: add quiescent state between work items

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Message-ID: <20141007134329.GA4880@linux.vnet.ibm.com>
Date:	Tue, 7 Oct 2014 06:43:29 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Jiri Pirko <jiri@...nulli.us>
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

On Tue, Oct 07, 2014 at 09:29:42AM +0200, Jiri Pirko wrote:
> 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.

Hello, Jiri,

Older kernels can instead use rcu_note_context_switch().

							Thanx, Paul

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