In the following situation, scrub will calculate wrong parity to
overwrite 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 after raid56 read rebuild rbio->stripe_pages are all
correct recovered (0xcd for data stripes).
However when we check and repair parity, in
scrub_parity_check_and_repair(), we will appending 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 <quwen...@cn.fujitsu.com>
---
fs/btrfs/scrub.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 6832feece7a7..2a5458004279 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2957,7 +2957,6 @@ static void scrub_parity_check_and_repair(struct
scrub_parity *sparity)
struct btrfs_fs_info *fs_info = sctx->fs_info;
struct bio *bio;
struct btrfs_raid_bio *rbio;
- struct scrub_page *spage;
struct btrfs_bio *bbio = NULL;
u64 length;
int ret;
@@ -2987,9 +2986,6 @@ static void scrub_parity_check_and_repair(struct
scrub_parity *sparity)
if (!rbio)
goto rbio_out;
- list_for_each_entry(spage, &sparity->spages, list)
- raid56_add_scrub_pages(rbio, spage->page, spage->logical);
-
scrub_pending_bio_inc(sctx);
raid56_parity_submit_scrub_rbio(rbio);
return;
--
2.12.1
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