From: Matthew Wilcox <willy@infradead.org>
To: Anastasia Belova <abelova@astralinux.ru>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeelb@google.com>,
Muchun Song <muchun.song@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, lvc-project@linuxtesting.org
Subject: Re: [PATCH] mm: memcomtrol: add warning in case of rtpn = NULL
Date: Mon, 21 Aug 2023 15:25:53 +0100 [thread overview]
Message-ID: <ZONz8Zqwg4cuCGCe@casper.infradead.org> (raw)
In-Reply-To: <20230821142051.31889-1-abelova@astralinux.ru>
On Mon, Aug 21, 2023 at 05:20:51PM +0300, Anastasia Belova wrote:
> kzalloc_node may return NULL. So rtpn should be
> checked before dereference in mem_cgroup_init.
What good will this do?
>
> rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL, node);
> + WARN_ON(!rtpn);
>
> rtpn->rb_root = RB_ROOT;
so you'll get a warning right before you get a crash, which will provide
exactly the same information. And you'd already have a warning that
the memory allocation had failed (because __GFP_NOWARN wasn't set).
So you've increased the amount of data from 2 dumps to 3 without providing
any neww information.
If you _did_ something to avoid the crash, there might be a point to
this, but the fact is that small GFP_KERNEL allocations _don't_ fail.
You need to teach your tool that, or you'll be overwhelmed with
false positives.
next prev parent reply other threads:[~2023-08-21 14:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-21 14:20 Anastasia Belova
2023-08-21 14:25 ` Matthew Wilcox [this message]
2023-08-21 14:30 ` Michal Hocko
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