[PATCH v2 02/12] block: prevent race condition on bi_status in __bio_chain_endio
zhangshida <[email protected]>
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From: Shida Zhang <[email protected]> Andreas point out that multiple completions can race setting bi_status. The check (parent->bi_status) and the subsequent write are not an atomic operation. The value of parent->bi_status could have changed between the time you read it for the if check and the time you write to it. So we use cmpxchg to fix the race, as suggested by Christoph. Suggested-by: Andreas Gruenbacher <[email protected]> Suggested-by: Christoph Hellwig <[email protected]> Signed-off-by: Shida Zhang <[email protected]> --- block/bio.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/block/bio.c b/block/bio.c index 55c2c1a0020..aa43435c15f 100644 --- a/block/bio.c +++ b/block/bio.c @@ -313,9 +313,12 @@ EXPORT_SYMBOL(bio_reset); static struct bio *__bio_chain_endio(struct bio *bio) { struct bio *parent = bio->bi_private; + blk_status_t *status = &parent->bi_status; + blk_status_t new_status = bio->bi_status; + + if (new_status != BLK_STS_OK) + cmpxchg(status, BLK_STS_OK, new_status); - if (bio->bi_status && !parent->bi_status) - parent->bi_status = bio->bi_status; bio_put(bio); return parent; } -- 2.34.1