linux-kernel - Re: [PATCH v3] Crash: add lock to serialize crash hotplug handling

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Message-ID: <xhsmhy1gqu1cu.mognet@vschneid.remote.csb>
Date:   Thu, 28 Sep 2023 10:51:45 +0200
From:   Valentin Schneider <vschneid@...hat.com>
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     kexec@...ts.infradead.org, akpm@...ux-foundation.org,
        eric.devolder@...cle.com, sourabhjain@...ux.ibm.com,
        Baoquan He <bhe@...hat.com>
Subject: Re: [PATCH v3] Crash: add lock to serialize crash hotplug handling

On 26/09/23 20:09, Baoquan He wrote:
> Eric reported that handling corresponding crash hotplug event can be
> failed easily when many memory hotplug event are notified in a short
> period. They failed because failing to take __kexec_lock.
>
> =======
> [   78.714569] Fallback order for Node 0: 0
> [   78.714575] Built 1 zonelists, mobility grouping on.  Total pages: 1817886
> [   78.717133] Policy zone: Normal
> [   78.724423] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
> [   78.727207] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
> [   80.056643] PEFILE: Unsigned PE binary
> =======
>
> The memory hotplug events are notified very quickly and very many,
> while the handling of crash hotplug is much slower relatively. So the
> atomic variable __kexec_lock and kexec_trylock() can't guarantee the
> serialization of crash hotplug handling.
>
> Here, add a new mutex lock __crash_hotplug_lock to serialize crash
> hotplug handling specifically. This doesn't impact the usage of
> __kexec_lock.
>
> Signed-off-by: Baoquan He <bhe@...hat.com>

Reviewed-by: Valentin Schneider <vschneid@...hat.com>