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block: remove management of bi_remaining when restoring original bi_end_io

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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>
This commit is contained in:
Mike Snitzer
2015-05-22 09:14:03 -04:00
committed by Jens Axboe
parent b04a5636a6
commit 326e1dbb57
12 changed files with 27 additions and 66 deletions
Download Patch File Download Diff File Expand all files Collapse all files
block/bio-integrity.c
+2 -2
View File
@@ -361,7 +361,7 @@ static void bio_integrity_verify_fn(struct work_struct *work)
/* Restore original bio completion handler */
bio->bi_end_io = bip->bip_end_io;
bio_endio_nodec(bio, error);
bio_endio(bio, error);
}
/**
@@ -388,7 +388,7 @@ void bio_integrity_endio(struct bio *bio, int error)
*/
if (error) {
bio->bi_end_io = bip->bip_end_io;
bio_endio_nodec(bio, error);
bio_endio(bio, error);
return;
}
block/bio.c
+14 -21
View File
@@ -303,6 +303,17 @@ static void bio_chain_endio(struct bio *bio, int error)
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 @@ static inline bool bio_remaining_done(struct bio *bio)
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;
}
@@ -1808,26 +1821,6 @@ void bio_endio(struct bio *bio, int error)
}
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