[PATCH AUTOSEL for 4.14 056/161] Btrfs: raid56: fix race between merge_bio and rbio_orig_end_io

Sasha Levin
2018-04-09T03:17:51Z

From: Liu Bo <bo.li.liu@oracle.com>

[ Upstream commit 7583d8d088ff2c323b1d4f15b191ca2c23d32558 ]

Before rbio_orig_end_io() goes to free rbio, rbio may get merged with
more bios from other rbios and rbio->bio_list becomes non-empty,
in that case, these newly merged bios don't end properly.

Once unlock_stripe() is done, rbio->bio_list will not be updated any
more and we can call bio_endio() on all queued bios.

It should only happen in error-out cases, the normal path of recover
and full stripe write have already set RBIO_RMW_LOCKED_BIT to disable
merge before doing IO, so rbio_orig_end_io() called by them doesn't
have the above issue.

Reported-by: Jérôme Carretero <cJ-ko@zougloub.eu>
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
fs/btrfs/raid56.c | 37 +++++++++++++++++++++++++------------
1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index dcab41157899..2e995e565633 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -858,10 +858,17 @@ static void __free_raid_bio(struct btrfs_raid_bio *rbio)
kfree(rbio);
}

-static void free_raid_bio(struct btrfs_raid_bio *rbio)
+static void rbio_endio_bio_list(struct bio *cur, blk_status_t err)
{
- unlock_stripe(rbio);
- __free_raid_bio(rbio);
+ struct bio *next;
+
+ while (cur) {
+ next = cur->bi_next;
+ cur->bi_next = NULL;
+ cur->bi_status = err;
+ bio_endio(cur);
+ cur = next;
+ }
}

/*
@@ -871,20 +878,26 @@ static void free_raid_bio(struct btrfs_raid_bio *rbio)
static void rbio_orig_end_io(struct btrfs_raid_bio *rbio, blk_status_t err)
{
struct bio *cur = bio_list_get(&rbio->bio_list);
- struct bio *next;
+ struct bio *extra;

if (rbio->generic_bio_cnt)
btrfs_bio_counter_sub(rbio->fs_info, rbio->generic_bio_cnt);

- free_raid_bio(rbio);
+ /*
+ * At this moment, rbio->bio_list is empty, however since rbio does not
+ * always have RBIO_RMW_LOCKED_BIT set and rbio is still linked on the
+ * hash list, rbio may be merged with others so that rbio->bio_list
+ * becomes non-empty.
+ * Once unlock_stripe() is done, rbio->bio_list will not be updated any
+ * more and we can call bio_endio() on all queued bios.
+ */
+ unlock_stripe(rbio);
+ extra = bio_list_get(&rbio->bio_list);
+ __free_raid_bio(rbio);

- while (cur) {
- next = cur->bi_next;
- cur->bi_next = NULL;
- cur->bi_status = err;
- bio_endio(cur);
- cur = next;
- }
+ rbio_endio_bio_list(cur, err);
+ if (extra)
+ rbio_endio_bio_list(extra, err);
}

/*
--
2.15.1