Re: WARNING in mark_buffer_dirty

[Matthew Wilcox <willy@infradead.org>]

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?

>  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