commit d459d853c2edc793135e4bfa4e345c758f1cc859
author Dennis Zhou <dennis@kernel.org> Sat Oct 20 14:56:12 2018 -0400
committer Jens Axboe <axboe@kernel.dk> Sat Oct 20 15:39:55 2018 -0600
tree bef29425e5ddb78a788cca764e926b4f5601f473
parent b2c3fa546705944e748666b474ffdaebaec0569f

blkcg: reassociate bios when make_request() is called recursively

When submitting a bio, multiple recursive calls to make_request() may
occur. This causes the initial associate done in blkcg_bio_issue_check()
to be incorrect and reference the prior request_queue. This introduces
a helper to do reassociation when make_request() is recursively called.

Fixes: a7b39b4e961c ("blkcg: always associate a bio with a blkg")
Reported-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Tested-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

diff --git a/block/bio.c b/block/bio.c
index 17a8b0a..bbfeb4e 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -2084,6 +2084,26 @@ int bio_associate_create_blkg(struct request_queue *q, struct bio *bio)
 }
 
 /**
+ * bio_reassociate_blkg - reassociate a bio with a blkg from q
+ * @q: request_queue where bio is going
+ * @bio: target bio
+ *
+ * When submitting a bio, multiple recursive calls to make_request() may occur.
+ * This causes the initial associate done in blkcg_bio_issue_check() to be
+ * incorrect and reference the prior request_queue.  This performs reassociation
+ * when this situation happens.
+ */
+int bio_reassociate_blkg(struct request_queue *q, struct bio *bio)
+{
+	if (bio->bi_blkg) {
+		blkg_put(bio->bi_blkg);
+		bio->bi_blkg = NULL;
+	}
+
+	return bio_associate_create_blkg(q, bio);
+}
+
+/**
  * bio_disassociate_task - undo bio_associate_current()
  * @bio: target bio
  */

block/blk-core.c

diff --git a/block/blk-core.c b/block/blk-core.c
index cdfabc5..3ed6072 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2433,6 +2433,7 @@ blk_qc_t generic_make_request(struct bio *bio)
 			if (q)
 				blk_queue_exit(q);
 			q = bio->bi_disk->queue;
+			bio_reassociate_blkg(q, bio);
 			flags = 0;
 			if (bio->bi_opf & REQ_NOWAIT)
 				flags = BLK_MQ_REQ_NOWAIT;

include/linux/bio.h

diff --git a/include/linux/bio.h b/include/linux/bio.h
index f447b0e..b47c7f7 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -514,6 +514,7 @@ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg);
 int bio_associate_blkg_from_css(struct bio *bio,
 				struct cgroup_subsys_state *css);
 int bio_associate_create_blkg(struct request_queue *q, struct bio *bio);
+int bio_reassociate_blkg(struct request_queue *q, struct bio *bio);
 void bio_disassociate_task(struct bio *bio);
 void bio_clone_blkg_association(struct bio *dst, struct bio *src);
 #else	/* CONFIG_BLK_CGROUP */
@@ -522,6 +523,8 @@ static inline int bio_associate_blkg_from_css(struct bio *bio,
 { return 0; }
 static inline int bio_associate_create_blkg(struct request_queue *q,
 					    struct bio *bio) { return 0; }
+static inline int bio_reassociate_blkg(struct request_queue *q, struct bio *bio)
+{ return 0; }
 static inline void bio_disassociate_task(struct bio *bio) { }
 static inline void bio_clone_blkg_association(struct bio *dst,
 					      struct bio *src) { }