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    SubjectRe: [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@linux.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@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: b22ce2785d97 ("workqueue: cond_resched() after processing each work item")
    > >> > > Cc: <stable@vger.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@kernel.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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