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    SubjectRe: rcu, sched: WARNING: CPU: 30 PID: 23771 at kernel/rcu/tree_plugin.h:337 rcu_read_unlock_special+0x369/0x550()
    On Tue, Jan 27, 2015 at 05:08:21PM -0500, Sasha Levin wrote:
    > On 01/27/2015 05:03 PM, Paul E. McKenney wrote:
    > > On Mon, Jan 26, 2015 at 10:08:04AM +0800, Lai Jiangshan wrote:
    > >> > On 01/25/2015 05:18 AM, Paul E. McKenney wrote:
    > >> >
    > >>> > >
    > >>> > > Good point! In my scenario, CPU 0 would not yet have switched away from
    > >>> > > Task A. Hmmm... Yet Sasha really does see this failure. Will give it
    > >>> > > some more thought.
    > >>> > >
    > >>> > > Any ideas?
    > >> >
    > >> > I don't known which commit was merged from the rcu-git-tree in Sasha's test
    > >> > I try to review it.
    > > If I had to guess, it would be 1d082fd06188 (Remove local_irq_disable()
    > > in rcu_preempt_note_context_switch()), though his finding this might be
    > > more directly related to increases in trinity's levels of stress.
    >
    > Quick update from my end: I've stopped seeing this warning, but I've also stopped
    > seeing warnings for the other RCU issue I've reported (https://lkml.org/lkml/2015/1/22/676)
    > so I'm slightly unhappy about that.

    Another approach would be to remove that patch and then revert 1d082fd06188.

    Either way, may I have your Tested-by?

    > >> > We can fallback to git-bitsect if the reviews fails.
    > > One (very unlikely) possibility is that Sasha's compiler is ignoring the
    > > barrier() in rcu_preempt_qs().
    >
    > I'm actually running the latest gcc (trunk) as well, so it's very possible that it was
    > doing something stupid.

    Hmmmm... Could you please send along the assembly output for rcu_preempt_qs()?

    Thanx, Paul



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