btrfs: scrub: Don't append on-disk pages for raid56 scrub
In the following situation, scrub will calculate wrong parity to
overwrite the correct one:
RAID5 full stripe:
Before
| Dev 1 | Dev 2 | Dev 3 |
| Data stripe 1 | Data stripe 2 | Parity Stripe |
--------------------------------------------------- 0
| 0x0000 (Bad) | 0xcdcd | 0x0000 |
--------------------------------------------------- 4K
| 0xcdcd | 0xcdcd | 0x0000 |
...
| 0xcdcd | 0xcdcd | 0x0000 |
--------------------------------------------------- 64K
After scrubbing dev3 only:
| Dev 1 | Dev 2 | Dev 3 |
| Data stripe 1 | Data stripe 2 | Parity Stripe |
--------------------------------------------------- 0
| 0xcdcd (Good) | 0xcdcd | 0xcdcd (Bad) |
--------------------------------------------------- 4K
| 0xcdcd | 0xcdcd | 0x0000 |
...
| 0xcdcd | 0xcdcd | 0x0000 |
--------------------------------------------------- 64K
The reason is that after raid56 read rebuild rbio->stripe_pages are all
correctly recovered (0xcd for data stripes).
However when we check and repair parity in
scrub_parity_check_and_repair(), we will append pages in sparity->spages
list to rbio->bio_pages[], which contains old on-disk data.
And when we submit parity data to disk, we calculate parity using
rbio->bio_pages[] first, if rbio->bio_pages[] not found, then fallback
to rbio->stripe_pages[].
The patch fix it by not appending pages from sparity->spages.
So finish_parity_scrub() will use rbio->stripe_pages[] which is correct.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
1 file changed