linux-kernel - Re: [BUG] WARNING in bdev

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Message-ID: <vwsalkqqm3gaxy5olc7nuolwrv62igdvi6s3hlp2sj2euizlzk@xdkfk6s3br22>
Date: Tue, 10 Jun 2025 10:02:42 +0200
From: Jan Kara <jack@...e.cz>
To: Matthew Wilcox <willy@...radead.org>
Cc: Jan Kara <jack@...e.cz>, Xianying Wang <wangxianying546@...il.com>, 
	viro@...iv.linux.org.uk, brauner@...nel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] WARNING in bdev_getblk

On Mon 09-06-25 21:48:49, Matthew Wilcox wrote:
> On Mon, Jun 09, 2025 at 03:54:01PM +0200, Jan Kara wrote:
> > Hi!
> > 
> > On Mon 09-06-25 16:39:15, Xianying Wang wrote:
> > > 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.
> > 
> > Ah, this is a warning about GFP_NOFAIL allocation from direct reclaim:
> 
> It's the same discussion we had at LSFMM.  It seems like we have a lot
> of "modified syzkaller" people trying this kind of thing.

Well, yes, it's from modified syzkaller and I'm not going to run the
reproducer but in this case it's clear just from the stacktrace what the
problem is and it looks like a valid (although relatively minor) issue.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR