From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, tglx@linutronix.de,
linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
frederic@kernel.org
Subject: Re: [PATCH 0/6] sched: TTWU, IPI, and assorted stuff
Date: Mon, 15 Jun 2020 09:23:30 -0700 [thread overview]
Message-ID: <20200615162330.GF2723@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200615125654.678940605@infradead.org>
On Mon, Jun 15, 2020 at 02:56:54PM +0200, Peter Zijlstra wrote:
> Hi,
>
> So Paul reported rcutorture hitting a NULL dereference, and patch #1 fixes it.
>
> Now, patch #1 is obviously correct, but I can't explain how exactly it leads to
> the observed NULL pointer dereference. The NULL pointer deref happens in
> find_matching_se()'s last while() loop when is_same_group() fails even though
> both parents are NULL.
My bisection of yet another bug sometimes hits the scheduler NULL pointer
dereference on older commits. I will try out patch #2.
Whether this is reassuring or depressing, I have no idea. :-/
> The only explanation I have for that is that we just did an activate_task()
> while: 'task_cpu(p) != cpu_of(rq)', because then 'p->se.cfs_rq' doesn't match.
> However, I can't see how the lack of #1 would lead to that. Never-the-less,
> patch #2 adds assertions to warn us of this case.
>
> Patch #3 is a trivial rename that ought to eradicate some confusion.
>
> The last 3 patches is what I ended up with for cleaning up the whole
> smp_call_function/irq_work/ttwu thing more.
Would it be possible to allow a target CPU # on those instances of
__call_single_data? This is extremely helpful for debugging lost
smp_call_function*() calls.
Thanx, Paul
next prev parent reply other threads:[~2020-06-15 16:23 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-15 12:56 [PATCH 0/6] sched: TTWU, IPI, and assorted stuff Peter Zijlstra
2020-06-15 12:56 ` [PATCH 1/6] sched: Fix ttwu_queue_cond() Peter Zijlstra
2020-06-15 13:34 ` Peter Zijlstra
2020-06-15 16:45 ` Paul E. McKenney
2020-06-15 22:58 ` Paul E. McKenney
2020-06-22 9:11 ` Mel Gorman
2020-06-22 9:41 ` Peter Zijlstra
2020-06-15 12:56 ` [PATCH 2/6] sched: Verify some SMP assumptions Peter Zijlstra
2020-06-15 12:56 ` [PATCH 3/6] sched: s/WF_ON_RQ/WQ_ON_CPU/ Peter Zijlstra
2020-06-22 9:13 ` Mel Gorman
2020-06-15 12:56 ` [PATCH 4/6] smp, irq_work: Continue smp_call_function*() and irq_work*() integration Peter Zijlstra
2020-06-15 12:56 ` [PATCH 5/6] irq_work: Cleanup Peter Zijlstra
2020-06-16 15:16 ` Petr Mladek
2020-06-15 12:57 ` [PATCH 6/6] smp: Cleanup smp_call_function*() Peter Zijlstra
2020-06-15 14:34 ` Jens Axboe
2020-06-15 16:04 ` Daniel Thompson
2020-06-17 8:23 ` Christoph Hellwig
2020-06-17 9:00 ` Peter Zijlstra
2020-06-17 11:04 ` Peter Zijlstra
2020-06-18 6:51 ` Christoph Hellwig
2020-06-18 16:25 ` Peter Zijlstra
2020-06-15 16:23 ` Paul E. McKenney [this message]
2020-06-15 16:40 ` [PATCH 0/6] sched: TTWU, IPI, and assorted stuff Peter Zijlstra
2020-06-15 17:21 ` Paul E. McKenney
2020-06-15 19:11 ` Peter Zijlstra
2020-06-15 19:55 ` Paul E. McKenney
2020-06-16 16:31 ` Paul E. McKenney
2020-06-16 17:04 ` Peter Zijlstra
2020-06-16 17:17 ` Peter Zijlstra
2020-06-16 17:53 ` Paul E. McKenney
2020-06-19 13:44 ` Peter Zijlstra
2020-06-19 17:20 ` Paul E. McKenney
2020-06-19 17:48 ` Paul E. McKenney
2020-06-19 18:11 ` Peter Zijlstra
2020-06-19 18:46 ` Paul E. McKenney
2020-06-20 18:46 ` Paul E. McKenney
2020-06-16 17:51 ` Paul E. McKenney
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