[PATCH] bcache: fix double bio_endio completion in detached_dev_end_io

zhangshida
2026-01-15T07:48:40Z

From: Shida Zhang <zhangshida@kylinos.cn>

Commit 53280e398471 ("bcache: fix improper use of bi_end_io") attempted
to fix up bio completions by replacing manual bi_end_io calls with
bio_endio(). However, it introduced a double-completion bug in the
detached_dev path.

In a normal completion path, the call stack is:
blk_update_request
bio_endio(bio)
bio->bi_end_io(bio) -> detached_dev_end_io
bio_endio(bio) <- BUG: second call

To fix this, detached_dev_end_io() must manually call the next completion
handler in the chain.

However, in detached_dev_do_request(), if a discard is unsupported, the
bio is rejected before being submitted to the lower level. In this case,
we can use the standard bio_endio().

detached_dev_do_request
bio_endio(bio) <- Correct: starts completion for
unsubmitted bio

Fixes: 53280e398471 ("bcache: fix improper use of bi_end_io")
Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
---
drivers/md/bcache/request.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 82fdea7dea7..ec712b5879f 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -1104,7 +1104,14 @@ static void detached_dev_end_io(struct bio *bio)
}

kfree(ddip);
- bio_endio(bio);
+ /*
+ * This is an exception where bio_endio() cannot be used.
+ * We are already called from within a bio_endio() stack;
+ * calling it again here would result in a double-completion
+ * (decrementing bi_remaining twice). We must call the
+ * original completion routine directly.
+ */
+ bio->bi_end_io(bio);
}

static void detached_dev_do_request(struct bcache_device *d, struct bio *bio,
@@ -1136,7 +1143,7 @@ static void detached_dev_do_request(struct bcache_device *d, struct bio *bio,

if ((bio_op(bio) == REQ_OP_DISCARD) &&
!bdev_max_discard_sectors(dc->bdev))
- detached_dev_end_io(bio);
+ bio_endio(bio);
else
submit_bio_noacct(bio);
}
--
2.34.1