linux-kernel - Re: mm: swap: locking in release

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Message-ID: <dc5eb22d-5389-bacb-3756-253e774a8394@nokia.com>
Date:   Tue, 5 Apr 2022 13:36:09 +0200
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Alexander Duyck <alexanderduyck@...com>,
        Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>, Yu Zhao <yuzhao@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Lee Schermerhorn <lee.schermerhorn@...com>,
        Sasha Levin <sashal@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: mm: swap: locking in release_pages()

Hello Michal,

thanks for the quick reply!

On 05/04/2022 12:43, Michal Hocko wrote:
>> 1. Crash of v5.4.170 on an ARM32 machine:
>>
>> Unable to handle kernel NULL pointer dereference at virtual address 00000104
>> pgd = e138149d
>> [00000104] *pgd=84d2fd003, *pmd=8ffd6f003
>> Internal error: Oops: a07 [#1] PREEMPT SMP ARM
>> ...
>> CPU: 1 PID: 6172 Comm: AaSysInfoRColle Tainted: G    B      O      5.4.170-... #1
>> Hardware name: Keystone
>> PC is at release_pages+0x194/0x358
>> LR is at release_pages+0x10c/0x358
> Which LOC does this correspond to? (faddr2line should give you a nice
> output).

Sorry, I forgot this info in the initial report:

this is indeed the del_page_from_lru_list() in this crash. So it's either two different ->lru_lock
or some other code path doesn't take lru_lock at all...

-- 
Best regards,
Alexander Sverdlin.