linux-kernel - Re: Kernel BUG at fs/mpage.c:489

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Date:	Wed, 13 Feb 2008 20:24:03 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Bart Dopheide <dopheide@....nl>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Jens Axboe <jens.axboe@...cle.com>,
	Bartlomiej Zolnierkiewicz <mzolnier@...il.com>
Subject: Re: Kernel BUG at fs/mpage.c:489

On Wednesday 13 February 2008 20:01, Andrew Morton wrote:
> On Wed, 13 Feb 2008 08:26:27 +0100 Bart Dopheide <dopheide@....nl> wrote:
> > On Wed, Feb 13, 2008 at 12:05:45PM +1100, Nick Piggin wrote:
> > :)On Wednesday 13 February 2008 08:50, Alan Cox wrote:
> > :)> Almost certainly a hardware fail of some sort.
> > :)
> > :)Right, but the kernel shouldn't go bug...
> >
> > Indeed, that's why I'm reporting.
> >
> > :)I don't have a copy of your exact source code... which condition in
> > :)__mpage_writepage went BUG?
> >
> > BUG_ON(buffer_locked(bh));
> >
> > In a bit of context:
> > 482:    if (page_has_buffers(page)) {
> > 483:            struct buffer_head *head = page_buffers(page);
> > 484:            struct buffer_head *bh = head;
> > 485:
> > 486:            /* If they're all mapped and dirty, do it */
> > 487:            page_block = 0;
> > 488:            do {
> > 489:                    BUG_ON(buffer_locked(bh));
> > 490:                    if (!buffer_mapped(bh)) {
> > 491:                            /*
> > 492:                             * unmapped dirty buffers are created by
> > 493:                             * __set_page_dirty_buffers -> mmapped
> > data 494:                             */
> > 495:                            if (buffer_dirty(bh))
> > 496:                                    goto confused;
> > 497:                            if (first_unmapped == blocks_per_page)
> > 498:                                    first_unmapped = page_block;
> > 499:                            continue;
> > 500:                    }
>
> Probably means that either fat, IDE, block or fs/buffer.c failed to unlock
> a buffer_head when the IO error happened.  It's unlikely to be fat.

Yes that looks like it would be the problem. I can't really
see anything in buffer.c that would do it... 

BTW is it really true that the buffer can never be locked by
anything else at this point? What about fsync_buffers_list?
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