linux-kernel - Re: WARNING in mark_buffer

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Date: Mon, 18 Mar 2024 11:12:22 +0100
From: Jan Kara <jack@...e.cz>
To: Matthew Wilcox <willy@...radead.org>
Cc: cheung wall <zzqq0103.hey@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: WARNING in mark_buffer_dirty

On Sat 16-03-24 04:54:10, Matthew Wilcox wrote:
> 
> This might be an iomap bug, so adding Christoph & Darrick.
> 
> On Sat, Mar 16, 2024 at 12:29:36PM +0800, cheung wall wrote:
> > HEAD commit: 0dd3ee31125508cd67f7e7172247f05b7fd1753a  (tag: v6.7)
> > WARNING: CPU: 0 PID: 2920 at fs/buffer.c:1176
> > mark_buffer_dirty+0x232/0x290
> 
> This is WARN_ON_ONCE(!buffer_uptodate(bh)), so we're trying to mark a
> buffer dirty when that buffer is not uptodate.
> 
> > RIP: 0010:mark_buffer_dirty+0x232/0x290
> > fs/buffer.c:1176
> > Call Trace:
> >  <TASK>
> >  __block_commit_write+0xe9/0x200
> > fs/buffer.c:2191
> 
> ... but line 2190 and 91 are:
> 
>                         set_buffer_uptodate(bh);
>                         mark_buffer_dirty(bh);
> 
> and the folio is locked.  So how do we clear the uptodate flag on the
> buffer without the folio locked?

Given this happens on block device page cache, I can imagine there's
someone operating on the cache directly using buffer heads without locking
the page. Filesystems do this all the time. I don't see the reproducer doing
anything like that but who knows...

								Honza

> >  block_write_end+0xb1/0x1f0
> > fs/buffer.c:2267
> >  iomap_write_end+0x461/0x8c0
> > fs/iomap/buffered-io.c:857
> >  iomap_write_iter
> > fs/iomap/buffered-io.c:938
> > [inline]
> >  iomap_file_buffered_write+0x4eb/0x800
> > fs/iomap/buffered-io.c:987
> >  blkdev_buffered_write
> > block/fops.c:646
> > [inline]
> >  blkdev_write_iter+0x4ae/0xa40
> > block/fops.c:696
> >  call_write_iter
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR