From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@kernel.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 18:40:48 +0200 [thread overview]
Message-ID: <20200615164048.GC2531@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200615162330.GF2723@paulmck-ThinkPad-P72>
On Mon, Jun 15, 2020 at 09:23:30AM -0700, Paul E. McKenney wrote:
> 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.
Thanks! I've got 16*TREE03 running since this morning, so far so nothing :/
(FWIW that's 16/9 times overcommit, idle time fluctuates around 10%).
> Whether this is reassuring or depressing, I have no idea. :-/
Worrysome at least, I don't trust stuff I can't explain.
> > 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.
target or source ? Either would be possible, perhaps even both. We have
a spare u32 in __call_single_node.
Something like the below on top of 1-4. If we want to keep this, we
should probably stick it under some CONFIG_DBUG thing or other.
--- a/include/linux/smp_types.h
+++ b/include/linux/smp_types.h
@@ -61,6 +61,7 @@ struct __call_single_node {
unsigned int u_flags;
atomic_t a_flags;
};
+ u16 src, dst;
};
#endif /* __LINUX_SMP_TYPES_H */
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -135,8 +135,14 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(cal
void __smp_call_single_queue(int cpu, struct llist_node *node)
{
+ struct __call_single_node *n =
+ container_of(node, struct __call_single_node, llist);
+
WARN_ON_ONCE(cpu == smp_processor_id());
+ n->src = smp_processor_id();
+ n->dst = cpu;
+
/*
* The list addition should be visible before sending the IPI
* handler locks the list to pull the entry off it because of
next prev parent reply other threads:[~2020-06-15 16:41 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 ` [PATCH 0/6] sched: TTWU, IPI, and assorted stuff Paul E. McKenney
2020-06-15 16:40 ` Peter Zijlstra [this message]
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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