blk-flush: fix invalid BUG_ON in blk_insert_flush
Jeff Moyer [Mon, 17 Oct 2011 10:57:22 +0000 (12:57 +0200)]
commit 834f9f61a525d2f6d3d0c93894e26326c8d3ceed upstream.

A user reported a regression due to commit
4853abaae7e4a2af938115ce9071ef8684fb7af4 (block: fix flush
machinery for stacking drivers with differring flush flags).
Part of the problem is that blk_insert_flush required a
single bio be attached to the request.  In reality, having
no attached bio is also a valid case, as can be observed with
an empty flush.

[1] http://www.redhat.com/archives/dm-devel/2011-September/msg00154.html

Reported-by: Christophe Saout <christophe@saout.de>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

block/blk-flush.c

index 491eb30..89ae3b9 100644 (file)
@@ -320,7 +320,7 @@ void blk_insert_flush(struct request *rq)
                return;
        }
 
-       BUG_ON(!rq->bio || rq->bio != rq->biotail);
+       BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
 
        /*
         * If there's data but flush is not necessary, the request can be