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Message-Id: <20220418205531.2e4ed0f72e0e537ef55c6468@linux-foundation.org>
Date: Mon, 18 Apr 2022 20:55:31 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Miaohe Lin <linmiaohe@...wei.com>
Cc: <vbabka@...e.cz>, <pintu@...eaurora.org>,
<charante@...eaurora.org>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>,
David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 09/12] mm: compaction: avoid possible NULL pointer
dereference in kcompactd_cpu_online
Please cc David H on memhotplug stuff.
On Mon, 18 Apr 2022 22:12:50 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:
> It's possible that kcompactd_run could fail to run kcompactd for a hot
> added node and leave pgdat->kcompactd as NULL. So pgdat->kcompactd should
> be checked here to avoid possible NULL pointer dereference.
>
> ..
>
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -3052,7 +3052,8 @@ static int kcompactd_cpu_online(unsigned int cpu)
>
> if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
> /* One of our CPUs online: restore mask */
> - set_cpus_allowed_ptr(pgdat->kcompactd, mask);
> + if (pgdat->kcompactd)
> + set_cpus_allowed_ptr(pgdat->kcompactd, mask);
> }
> return 0;
> }
Why not fail to bring the node online if kcompactd_run() failed?
Also, should we panic the system if kcompactd_run() failed in
kcompactd_init()?
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