linux-kernel - Re: [PATCH] fat: fix data-race between fat12_ent_put() and fat_mirror

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Message-ID: <20250902132459.44-1-anmuxixixi@gmail.com>
Date: Tue,  2 Sep 2025 21:24:59 +0800
From: YangWen <anmuxixixi@...il.com>
To: hirofumi@...l.parknet.co.jp
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fat: fix data-race between fat12_ent_put() and fat_mirror_bhs()

Hi,

OGAWA Hirofumi wrote:
> Sounds like strange. FAT driver never read the mirror FAT area in
> runtime. Why did you think the mirror FAT affect to it?

Thanks for raising this point.

FAT driver itself never reads the mirror FAT at
runtime, so this race does not directly cause runtime corruption.

However, if the primary FAT on disk becomes damaged, user-space tools
such as fsck_msdos will consult the backup FAT copies in order to
repair it.  In that scenario, keeping the primary and backup FAT copies
consistent is important.  If they diverge due to a race between
fat12_ent_put() and fat_mirror_bhs(), recovery by fsck_msdos
may become unreliable.

So my intention was not to fix a runtime problem, but rather to prevent
unnecessary inconsistencies between the primary and backup FAT copies,
which can help later recovery tools work as expected.

Thanks.