FAILED: patch "[PATCH] block, bfq: fix procress reference leakage for bfqq in merge" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 73aeab373557fa6ee4ae0b742c6211ccd9859280
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024100232-unheated-trailing-4528@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

73aeab373557 ("block, bfq: fix procress reference leakage for bfqq in merge chain") 9778369a2d6c ("block, bfq: split sync bfq_queues on a per-actuator basis") 246cf66e300b ("block, bfq: fix uaf for bfqq in bfq_exit_icq_bfqq") 337366e02b37 ("block, bfq: replace 0/1 with false/true in bic apis") 64dc8c732f5c ("block, bfq: fix possible uaf for 'bfqq->bic'") dc469ba2e790 ("block/bfq: Use the new blk_opf_t type")
4e54a2493e58 ("bfq: Get rid of __bio_blkcg() usage")
09f871868080 ("bfq: Track whether bfq_group is still online") ea591cd4eb27 ("bfq: Update cgroup information before merging bio") 3bc5e683c67d ("bfq: Split shared queues on move between cgroups") f6bad159f5d5 ("block/bfq-iosched.c: use "false" rather than "BLK_RW_ASYNC"") a0725c22cd84 ("bfq: use bfq_bic_lookup in bfq_limit_depth") 1f18b7005b49 ("bfq: Limit waker detection in time")
76f1df88bbc2 ("bfq: Limit number of requests consumed by each cgroup") 44dfa279f117 ("bfq: Store full bitmap depth in bfq_data")
ae0f1a732f4a ("blk-mq: Stop using pointers for blk_mq_tags bitmap tags") e155b0c238b2 ("blk-mq: Use shared tags for shared sbitmap support") 645db34e5050 ("blk-mq: Refactor and rename blk_mq_free_map_and_{requests->rqs}()") 63064be150e4 ("blk-mq: Add blk_mq_alloc_map_and_rqs()")
a7e7388dced4 ("blk-mq: Add blk_mq_tag_update_sched_shared_sbitmap()")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 73aeab373557fa6ee4ae0b742c6211ccd9859280 Mon Sep 17 00:00:00 2001
From: Yu Kuai <[email protected]>
Date: Mon, 9 Sep 2024 21:41:49 +0800
Subject: [PATCH] block, bfq: fix procress reference leakage for bfqq in merge
chain
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Original state:

Process 1 Process 2 Process 3 Process 4
(BIC1) (BIC2) (BIC3) (BIC4)
Λ | | |
\--------------\ \-------------\ \-------------\|
V V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
ref 0 1 2 4

After commit 0e456dba86c7 ("block, bfq: choose the last bfqq from merge chain in bfq_setup_cooperator()"), if P1 issues a new IO:

Without the patch:

Process 1 Process 2 Process 3 Process 4
(BIC1) (BIC2) (BIC3) (BIC4)
Λ | | |
\------------------------------\ \-------------\|
V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
ref 0 0 2 4

bfqq3 will be used to handle IO from P1, this is not expected, IO should be redirected to bfqq4;

With the patch:

-------------------------------------------
| |
Process 1 Process 2 Process 3 | Process 4
(BIC1) (BIC2) (BIC3) | (BIC4)
| | | |
\-------------\ \-------------\|
V V
bfqq1--------->bfqq2---------->bfqq3----------->bfqq4
ref 0 0 2 4

IO is redirected to bfqq4, however, procress reference of bfqq3 is still 2, while there is only P2 using it.

Fix the problem by calling bfq_merge_bfqqs() for each bfqq in the merge chain. Also change bfqq_merge_bfqqs() to return new_bfqq to simplify code.

index d5d39974c674..f4192d5411d2 100644
@@ -3129,10 +3129,12 @@ void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq)
 	bfq_put_queue(bfqq);
 }
 
-static void
-bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
-		struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
+static struct bfq_queue *bfq_merge_bfqqs(struct bfq_data *bfqd,
+					 struct bfq_io_cq *bic,
+					 struct bfq_queue *bfqq)
 {
+	struct bfq_queue *new_bfqq = bfqq->new_bfqq;
+
 	bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
 		(unsigned long)new_bfqq->pid);
 	/* Save weight raising and idle window of the merged queues */

@@ -3226,6 +3228,8 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
 	bfq_reassign_last_bfqq(bfqq, new_bfqq);
 
 	bfq_release_process_ref(bfqd, bfqq);
+
+	return new_bfqq;
 }
 
 static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,

@@ -3261,14 +3265,8 @@ static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
 		 * fulfilled, i.e., bic can be redirected to new_bfqq
 		 * and bfqq can be put.
 		 */
-		bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq,
-				new_bfqq);
-		/*
-		 * If we get here, bio will be queued into new_queue,
-		 * so use new_bfqq to decide whether bio and rq can be
-		 * merged.
-		 */
-		bfqq = new_bfqq;
+		while (bfqq != new_bfqq)
+			bfqq = bfq_merge_bfqqs(bfqd, bfqd->bio_bic, bfqq);
 
 		/*
 		 * Change also bqfd->bio_bfqq, as

@@ -5705,9 +5703,7 @@ bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 	 * state before killing it.
 	 */
 	bfqq->bic = bic;
-	bfq_merge_bfqqs(bfqd, bic, bfqq, new_bfqq);
-
-	return new_bfqq;
+	return bfq_merge_bfqqs(bfqd, bic, bfqq);
 }
 
 /*

@@ -6162,6 +6158,7 @@ static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
 	bool waiting, idle_timer_disabled = false;
 
 	if (new_bfqq) {
+		struct bfq_queue *old_bfqq = bfqq;
 		/*
 		 * Release the request's reference to the old bfqq
 		 * and make sure one is taken to the shared queue.

@@ -6178,18 +6175,18 @@ static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
 		 * new_bfqq.
 		 */
 		if (bic_to_bfqq(RQ_BIC(rq), true,
-				bfq_actuator_index(bfqd, rq->bio)) == bfqq)
-			bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
-					bfqq, new_bfqq);
+				bfq_actuator_index(bfqd, rq->bio)) == bfqq) {
+			while (bfqq != new_bfqq)
+				bfqq = bfq_merge_bfqqs(bfqd, RQ_BIC(rq), bfqq);
+		}
 
-		bfq_clear_bfqq_just_created(bfqq);
+		bfq_clear_bfqq_just_created(old_bfqq);
 		/*
 		 * rq is about to be enqueued into new_bfqq,
 		 * release rq reference on bfqq
 		 */
-		bfq_put_queue(bfqq);
+		bfq_put_queue(old_bfqq);
 		rq->elv.priv[1] = new_bfqq;
-		bfqq = new_bfqq;
 	}
 
 	bfq_update_io_thinktime(bfqd, bfqq);