linux-kernel - [BUG] WARNING in bdev

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Message-ID: <CAOU40uAjmLO9f0LOGqPdVd5wpiFK6QaT+UwiNvRoBXhVnKcDbw@mail.gmail.com>
Date: Mon, 9 Jun 2025 16:39:15 +0800
From: Xianying Wang <wangxianying546@...il.com>
To: viro@...iv.linux.org.uk
Cc: brauner@...nel.org, jack@...e.cz, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [BUG] WARNING in bdev_getblk

Hi,

I encountered a kernel WARNING in the function bdev_getblk() when
fuzzing the Linux 6.12 kernel using Syzkaller. The crash occurs during
a block buffer allocation path, where __alloc_pages_noprof() fails
under memory pressure, and triggers a WARNING due to an internal
allocation failure.

Root Cause:

Code Path: The failure originates from the function bdev_getblk() in
fs/buffer.c, which attempts to allocate a new buffer via
grow_buffers() → grow_dev_folio() → __filemap_get_folio().
Memory Allocation Failure: Under specific memory pressure and
vm.zone_reclaim_mode settings, the internal call to alloc_pages() in
__alloc_pages_noprof() fails, resulting in the observed warning.

I recommend reviewing the block buffer allocation path in
bdev_getblk(), particularly how it handles allocation failures under
memory pressure.

This can be reproduced on:

HEAD commit:

commit adc218676eef25575469234709c2d87185ca223a

report: https://pastebin.com/raw/wqAeZJxF

console output : https://pastebin.com/raw/aLaVQpzR

kernel config : https://pastebin.com/x48ijkN8

C reproducer : https://pastebin.com/raw/whJgYnHk

Best regards,

Xianying