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From: Qian Cai <cai@lca.pw>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	peterz@infradead.org, mingo@redhat.com
Cc: akpm@linux-foundation.org, tglx@linutronix.de,
	thgarnie@google.com,  tytso@mit.edu, cl@linux.com,
	penberg@kernel.org, rientjes@google.com,  will@kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	 keescook@chromium.org
Subject: Re: [PATCH] mm/slub: fix a deadlock in shuffle_freelist()
Date: Mon, 16 Sep 2019 10:01:27 -0400
Message-ID: <1568642487.5576.152.camel@lca.pw> (raw)
In-Reply-To: <20190916090336.2mugbds4rrwxh6uz@linutronix.de>

On Mon, 2019-09-16 at 11:03 +0200, Sebastian Andrzej Siewior wrote:
> On 2019-09-13 12:27:44 [-0400], Qian Cai wrote:
> …
> > Chain exists of:
> >   random_write_wait.lock --> &rq->lock --> batched_entropy_u32.lock
> > 
> >  Possible unsafe locking scenario:
> > 
> >        CPU0                    CPU1
> >        ----                    ----
> >   lock(batched_entropy_u32.lock);
> >                                lock(&rq->lock);
> >                                lock(batched_entropy_u32.lock);
> >   lock(random_write_wait.lock);
> 
> would this deadlock still occur if lockdep knew that
> batched_entropy_u32.lock on CPU0 could be acquired at the same time
> as CPU1 acquired its batched_entropy_u32.lock?

I suppose that might fix it too if it can teach the lockdep the trick, but it
would be better if there is a patch if you have something in mind that could be
tested to make sure.


  reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-13 16:27 Qian Cai
2019-09-16  9:03 ` Sebastian Andrzej Siewior
2019-09-16 14:01   ` Qian Cai [this message]
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

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