[PATCH AUTOSEL 4.20 49/77] block: cover another queue enter recursion via BIO_QUEUE_ENTERED

* [PATCH AUTOSEL 4.20 49/77] block: cover another queue enter recursion via BIO_QUEUE_ENTERED
       [not found] <20190215020855.176727-1-sashal@kernel.org>
@ 2019-02-15  2:08 ` Sasha Levin
  2019-02-15  2:24   ` Tetsuo Handa
  2019-02-15  2:28   ` Ming Lei
  2019-02-15  2:08 ` [PATCH AUTOSEL 4.20 77/77] Revert "block: cover another queue enter recursion via BIO_QUEUE_ENTERED" Sasha Levin
  1 sibling, 2 replies; 5+ messages in thread
From: Sasha Levin @ 2019-02-15  2:08 UTC (permalink / raw)
  To: linux-kernel, stable
  Cc: Ming Lei, Tetsuo Handa, NeilBrown, Jens Axboe, Sasha Levin, linux-block

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 698cef173983b086977e633e46476e0f925ca01e ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-core.c  | 11 +++++++++++
 block/blk-merge.c | 10 ----------
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index deb56932f8c4..22260339f66f 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2449,7 +2449,18 @@ 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 7695034f4b87..adfe835ab258 100644
--- 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);
-- 
2.19.1


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