linux-kernel - Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

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Message-ID: <20191009142623.GE6681@dhcp22.suse.cz>
Date:   Wed, 9 Oct 2019 16:26:23 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Peter Oberparleiter <oberpar@...ux.ibm.com>
Cc:     Qian Cai <cai@....pw>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Petr Mladek <pmladek@...e.com>, akpm@...ux-foundation.org,
        sergey.senozhatsky.work@...il.com, rostedt@...dmis.org,
        peterz@...radead.org, linux-mm@...ck.org,
        john.ogness@...utronix.de, david@...hat.com,
        linux-kernel@...r.kernel.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

On Wed 09-10-19 15:56:32, Peter Oberparleiter wrote:
[...]
> A generic solution would be preferable from my point of view though,
> because otherwise each console driver owner would need to ensure that any
> lock taken in their console.write implementation is never held while
> memory is allocated/released.

Considering that console.write is called from essentially arbitrary code
path IIUC then all the locks used in this path should be pretty much
tail locks or console internal ones without external dependencies.
Otherwise we are in a whack a mole situation chasing very complex lock
chains.
-- 
Michal Hocko
SUSE Labs