From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-kernel@vger.kernel.org
Cc: linux-tip-commits@vger.kernel.org,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Qian Cai <cai@lca.pw>, Thomas Gleixner <tglx@linutronix.de>,
akpm@linux-foundation.org, cl@linux.com, keescook@chromium.org,
penberg@kernel.org, rientjes@google.com, thgarnie@google.com,
tytso@mit.edu, will@kernel.org, Ingo Molnar <mingo@kernel.org>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [tip: sched/urgent] sched/core: Avoid spurious lock dependencies
Date: Fri, 22 Nov 2019 21:01:22 +0100 [thread overview]
Message-ID: <20191122200122.wx7ltij2w7w37cbe@linutronix.de> (raw)
In-Reply-To: <157363958888.29376.9190587096871610849.tip-bot2@tip-bot2>
On 2019-11-13 10:06:28 [-0000], tip-bot2 for Peter Zijlstra wrote:
> sched/core: 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.
Peter, can it _really_ cause deadlocks? My understanding was that the
batched_entropy_u64.lock is a per-CPU lock and can _not_ cause a
deadlock because it can be always acquired on multiple CPUs
simultaneously (and it is never acquired cross-CPU).
Lockdep is simply not smart enough to see that and complains about it
like it would complain about a regular lock in this case.
Sebastian
next prev parent reply other threads:[~2019-11-22 20:01 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
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 [this message]
2019-11-22 20:20 ` Peter Zijlstra
2019-11-22 21:03 ` Qian Cai
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