linux-kernel - Re: [PATCH] mm/slub: fix a deadlock in shuffle

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Message-ID: <20190917071634.c7i3i6jg676ejiw5@linutronix.de>
Date:   Tue, 17 Sep 2019 09:16:35 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Qian Cai <cai@....pw>
Cc:     peterz@...radead.org, mingo@...hat.com, akpm@...ux-foundation.org,
        tglx@...utronix.de, thgarnie@...gle.com, tytso@....edu,
        cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        will@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        keescook@...omium.org
Subject: Re: [PATCH] mm/slub: fix a deadlock in shuffle_freelist()

On 2019-09-16 17:31:34 [-0400], Qian Cai wrote:
…
> get_random_u64() is also busted.
…
> [  753.486588]  Possible unsafe locking scenario:
> 
> [  753.493890]        CPU0                    CPU1
> [  753.499108]        ----                    ----
> [  753.504324]   lock(batched_entropy_u64.lock);
> [  753.509372]                                lock(&(&zone->lock)->rlock);
> [  753.516675]                                lock(batched_entropy_u64.lock);
> [  753.524238]   lock(random_write_wait.lock);
> [  753.529113] 
>                 *** DEADLOCK ***

This is the same scenario as the previous one in regard to the
batched_entropy_….lock.

Sebastian