linux-kernel - Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup

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Message-ID: <YQKyn8bKRblCDuND@casper.infradead.org>
Date:   Thu, 29 Jul 2021 14:52:31 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     hannes@...xchg.org, mhocko@...nel.org, vdavydov.dev@...il.com,
        akpm@...ux-foundation.org, shakeelb@...gle.com, guro@...com,
        alexs@...nel.org, richard.weiyang@...il.com,
        songmuchun@...edance.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing
 in mem_cgroup_init()

On Thu, Jul 29, 2021 at 08:57:54PM +0800, Miaohe Lin wrote:
> rtpn might be NULL in very rare case. We have better to check it before
> dereferencing it. Since memcg can live with NULL rb_tree_per_node in
> soft_limit_tree, warn this case and continue.

Why would we need to warn?  the GFP flags don't contain NOWARN, so
we already know an allocation failed.