Re: Please help me understand reiser4_writepage. Was Re: segfault mdadm --write-behind, 2.6.14-mm2 (was: Re: RAID1 ramdisk patch)

[Neil Brown <neilb@suse.de>]

On Tuesday November 22, sander@humilis.net wrote:
> 
> It doesn't crash or segfault anymore. It works with the bitmap file on
> tmpfs, but not yet on reiser4.
> 
> This is kernel 2.6.15-rc1-mm2 with your (Neil Brown's) patch.
> 
...
> [42949655.680000] md1: bitmap initialized from disk: read 0/4 pages, set 0 bits, status: 1
....

Ok, this is interesting... 'status: 1'.
That should be either 0 or a negative errno.

That is printed in bitmap_init_from_disk in drivers/md/bitmap.c

'ret' can only be '1' if that value is returned from 'write_page'
write_page (same file) can only return '1' if that is returned by
write_one_page (mm/page-writeback.c).
write_one_page can only return '1' from a_ops->writepage, which is
presumably
  reiser4_writepage in fs/reiser4/page_cache.c

This will only return an unchecked value from write_page_by_ent (if
REISER4_USE_ENTD is defined) or emergency_flush.
emergency_flush is in fs/reiser4/emergency_flush.c and it does indeed
return 1 in some circumstances, though I don't really know what
circumstances.

So there may well be something that md/bitmap is doing wrongly, but
reiser4_writepage should not be returning 1 in any case.

Could someone on reiserfs-dev help me understand when
reiser4_writepage returns '1' and what I might be doing to trigger
that?

Thanks,
NeilBrown

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