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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()
Date:   Thu, 10 Oct 2019 05:01:44 -0400
Message-Id: <6AAB77B5-092B-43E3-9F4B-0385DE1890D9@lca.pw>
References: <20191009162339.GI6681@dhcp22.suse.cz>
Cc:     Petr Mladek <pmladek@suse.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        sergey.senozhatsky.work@gmail.com, rostedt@goodmis.org,
        peterz@infradead.org, linux-mm@kvack.org,
        john.ogness@linutronix.de, akpm@linux-foundation.org,
        Vasily Gorbik <gor@linux.ibm.com>,
        Peter Oberparleiter <oberpar@linux.ibm.com>, david@redhat.com,
        linux-kernel@vger.kernel.org
In-Reply-To: <20191009162339.GI6681@dhcp22.suse.cz>
To:     Michal Hocko <mhocko@kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Oct 9, 2019, at 12:23 PM, Michal Hocko <mhocko@kernel.org> wrote:
>=20
> If this was only about the memory offline code then I would agree. But
> we are talking about any printk from the zone->lock context and that is
> a bigger deal. Besides that it is quite natural that the printk code
> should be more universal and allow to be also called from the MM
> contexts as much as possible. If there is any really strong reason this
> is not possible then it should be documented at least.

Where is the best place to document this? I am thinking about under the =E2=80=
=9Cstruct zone=E2=80=9D definition=E2=80=99s lock field in mmzone.h.

Does workaround this potential deadlock and fix a few lockdep false positive=
s for free count as a really strong reason?=