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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