block: remove management of bi_remaining when restoring original bi_end_io
Commit c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for
non-chains") regressed all existing callers that followed this pattern:
1) saving a bio's original bi_end_io
2) wiring up an intermediate bi_end_io
3) restoring the original bi_end_io from intermediate bi_end_io
4) calling bio_endio() to execute the restored original bi_end_io
The regression was due to BIO_CHAIN only ever getting set if
bio_inc_remaining() is called. For the above pattern it isn't set until
step 3 above (step 2 would've needed to establish BIO_CHAIN). As such
the first bio_endio(), in step 2 above, never decremented __bi_remaining
before calling the intermediate bi_end_io -- leaving __bi_remaining with
the value 1 instead of 0. When bio_inc_remaining() occurred during step
3 it brought it to a value of 2. When the second bio_endio() was
called, in step 4 above, it should've called the original bi_end_io but
it didn't because there was an extra reference that wasn't dropped (due
to atomic operations being optimized away since BIO_CHAIN wasn't set
upfront).
Fix this issue by removing the __bi_remaining management complexity for
all callers that use the above pattern -- bio_chain() is the only
interface that _needs_ to be concerned with __bi_remaining. For the
above pattern callers just expect the bi_end_io they set to get called!
Remove bio_endio_nodec() and also remove all bio_inc_remaining() calls
that aren't associated with the bio_chain() interface.
Also, the bio_inc_remaining() interface has been moved local to bio.c.
Fixes: c4cf5261 ("bio: skip atomic inc/dec of ->bi_remaining for non-chains")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/bio.c b/block/bio.c
index c2ff8a8..259197d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -303,6 +303,17 @@
bio_put(bio);
}
+/*
+ * Increment chain count for the bio. Make sure the CHAIN flag update
+ * is visible before the raised count.
+ */
+static inline void bio_inc_remaining(struct bio *bio)
+{
+ bio->bi_flags |= (1 << BIO_CHAIN);
+ smp_mb__before_atomic();
+ atomic_inc(&bio->__bi_remaining);
+}
+
/**
* bio_chain - chain bio completions
* @bio: the target bio
@@ -1756,8 +1767,10 @@
BUG_ON(atomic_read(&bio->__bi_remaining) <= 0);
- if (atomic_dec_and_test(&bio->__bi_remaining))
+ if (atomic_dec_and_test(&bio->__bi_remaining)) {
+ clear_bit(BIO_CHAIN, &bio->bi_flags);
return true;
+ }
return false;
}
@@ -1809,26 +1822,6 @@
EXPORT_SYMBOL(bio_endio);
/**
- * bio_endio_nodec - end I/O on a bio, without decrementing bi_remaining
- * @bio: bio
- * @error: error, if any
- *
- * For code that has saved and restored bi_end_io; thing hard before using this
- * function, probably you should've cloned the entire bio.
- **/
-void bio_endio_nodec(struct bio *bio, int error)
-{
- /*
- * If it's not flagged as a chain, we are not going to dec the count
- */
- if (bio_flagged(bio, BIO_CHAIN))
- bio_inc_remaining(bio);
-
- bio_endio(bio, error);
-}
-EXPORT_SYMBOL(bio_endio_nodec);
-
-/**
* bio_split - split a bio
* @bio: bio to split
* @sectors: number of sectors to split from the front of @bio