linux-ext4 - [bugzilla:219548] the kernel crashes when storing an EXT4 file system in a ZRAM device

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Message-ID: <20241212035826.GH2091455@google.com>
Date: Thu, 12 Dec 2024 12:58:26 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Theodore Ts'o <tytso@....edu>, Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <axboe@...nel.dk>,
	caiqingfu <baicaiaichibaicai@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	linux-ext4@...r.kernel.org, linux-block@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: [bugzilla:219548] the kernel crashes when storing an EXT4 file
 system in a ZRAM device

Hi,

We've got two reports [1] [2] (could be the same person) which
suggest that ext4 may change page content while the page is under
write().  The particular problem here the case when ext4 is on
the zram device.  zram compresses every page written to it, so if
the page content can be modified concurrently with zram's compression
then we can't really use zram with ext4.

Can you take a look please?

[1] https://bugzilla.kernel.org/show_bug.cgi?id=219548
[2] https://lore.kernel.org/linux-kernel/20241129115735.136033-1-baicaiaichibaicai@gmail.com