From: Qian Cai <cai@lca.pw>
To: Peter Zijlstra <peterz@infradead.org>
Cc: akpm@linux-foundation.org, bigeasy@linutronix.de,
tglx@linutronix.de, thgarnie@google.com, tytso@mit.edu,
cl@linux.com, penberg@kernel.org, rientjes@google.com,
mingo@redhat.com, will@kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, keescook@chromium.org
Subject: Re: [PATCH] sched: Avoid spurious lock dependencies
Date: Tue, 29 Oct 2019 07:10:34 -0400 [thread overview]
Message-ID: <EE57FDCF-E3CD-4A0D-B0CC-C3CBAA7EBCBD@lca.pw> (raw)
In-Reply-To: <20191001091837.GK4536@hirez.programming.kicks-ass.net>
> On Oct 1, 2019, at 5:18 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> Does the below adequately describe the situation?
>
> ---
> Subject: sched: Avoid spurious lock dependencies
>
> While seemingly harmless, __sched_fork() does hrtimer_init(), which,
> when DEBUG_OBJETS, can end up doing allocations.
>
> This then results in the following lock order:
>
> rq->lock
> zone->lock.rlock
> batched_entropy_u64.lock
>
> Which in turn causes deadlocks when we do wakeups while holding that
> batched_entropy lock -- as the random code does.
>
> Solve this by moving __sched_fork() out from under rq->lock. This is
> safe because nothing there relies on rq->lock, as also evident from the
> other __sched_fork() callsite.
>
> Fixes: b7d5dc21072c ("random: add a spinlock_t to struct batched_entropy")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/sched/core.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7880f4f64d0e..1832fc0fbec5 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6039,10 +6039,11 @@ void init_idle(struct task_struct *idle, int cpu)
> struct rq *rq = cpu_rq(cpu);
> unsigned long flags;
>
> + __sched_fork(0, idle);
> +
> raw_spin_lock_irqsave(&idle->pi_lock, flags);
> raw_spin_lock(&rq->lock);
>
> - __sched_fork(0, idle);
> idle->state = TASK_RUNNING;
> idle->se.exec_start = sched_clock();
> idle->flags |= PF_IDLE;
It looks like this patch has been forgotten forever. Do you need to repost, so Ingo might have a better chance to pick it up?
next prev parent reply other threads:[~2019-10-29 11:10 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-13 16:27 [PATCH] mm/slub: fix a deadlock in shuffle_freelist() Qian Cai
2019-09-16 9:03 ` Sebastian Andrzej Siewior
2019-09-16 14:01 ` Qian Cai
2019-09-16 19:51 ` Sebastian Andrzej Siewior
2019-09-16 21:31 ` Qian Cai
2019-09-17 7:16 ` Sebastian Andrzej Siewior
2019-09-18 19:59 ` Qian Cai
2019-09-25 9:31 ` Peter Zijlstra
2019-09-25 15:18 ` Qian Cai
2019-09-25 16:45 ` Peter Zijlstra
2019-09-26 12:29 ` Qian Cai
2019-10-01 9:18 ` [PATCH] sched: Avoid spurious lock dependencies Peter Zijlstra
2019-10-01 10:01 ` Valentin Schneider
2019-10-01 11:22 ` Qian Cai
2019-10-01 11:36 ` Srikar Dronamraju
2019-10-01 13:44 ` Peter Zijlstra
2019-10-29 11:10 ` Qian Cai [this message]
2019-10-29 12:44 ` Peter Zijlstra
2019-11-12 0:54 ` Qian Cai
2019-11-13 10:06 ` [tip: sched/urgent] sched/core: " tip-bot2 for Peter Zijlstra
2019-11-22 20:01 ` Sebastian Andrzej Siewior
2019-11-22 20:20 ` Peter Zijlstra
2019-11-22 21:03 ` Qian Cai
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