block: cover another queue enter recursion via BIO_QUEUE_ENTERED

Except for blk_queue_split(), bio_split() is used for splitting bio too,
then the remained bio is often resubmit to queue via generic_make_request().
So the same queue enter recursion exits in this case too. Unfortunatley
commit cd4a4ae4683dc2 doesn't help this case.

This patch covers the above case by setting BIO_QUEUE_ENTERED before calling
q->make_request_fn.

In theory the per-bio flag is used to simulate one stack variable, it is
just fine to clear it after q->make_request_fn is returned. Especially
the same bio can't be submitted from another context.

Fixes: cd4a4ae4683dc2 ("block: don't use blocking queue entered for recursive bio submits")
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: NeilBrown <neilb@suse.com>
Reviewed-by:  Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index 3c5f61c..1ccec27 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1083,7 +1083,18 @@ blk_qc_t generic_make_request(struct bio *bio)
                        /* Create a fresh bio_list for all subordinate requests */
                        bio_list_on_stack[1] = bio_list_on_stack[0];
                        bio_list_init(&bio_list_on_stack[0]);
+
+                       /*
+                        * Since we're recursing into make_request here, ensure
+                        * that we mark this bio as already having entered the queue.
+                        * If not, and the queue is going away, we can get stuck
+                        * forever on waiting for the queue reference to drop. But
+                        * that will never happen, as we're already holding a
+                        * reference to it.
+                        */
+                       bio_set_flag(bio, BIO_QUEUE_ENTERED);
                        ret = q->make_request_fn(q, bio);
+                       bio_clear_flag(bio, BIO_QUEUE_ENTERED);
 
                        /* sort new bios into those for a lower level
                         * and those for the same level

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 71e9ac0..d79a22f 100644 (file)
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -272,16 +272,6 @@ void blk_queue_split(struct request_queue *q, struct bio **bio)
                /* there isn't chance to merge the splitted bio */
                split->bi_opf |= REQ_NOMERGE;
 
-               /*
-                * Since we're recursing into make_request here, ensure
-                * that we mark this bio as already having entered the queue.
-                * If not, and the queue is going away, we can get stuck
-                * forever on waiting for the queue reference to drop. But
-                * that will never happen, as we're already holding a
-                * reference to it.
-                */
-               bio_set_flag(*bio, BIO_QUEUE_ENTERED);
-
                bio_chain(split, *bio);
                trace_block_split(q, split, (*bio)->bi_iter.bi_sector);
                generic_make_request(*bio);