[3/4] bfq: Split shared queues on move between cgroups

Commit Message

Jan Kara Jan. 21, 2022, 10:56 a.m. UTC

When bfqq is shared by multiple processes it can happen that one of the
processes gets moved to a different cgroup (or just starts submitting IO
for different cgroup). In case that happens we need to split the merged
bfqq as otherwise we will have IO for multiple cgroups in one bfqq and
we will just account IO time to wrong entities etc.

Similarly if the bfqq is scheduled to merge with another bfqq but the
merge didn't happen yet, cancel the merge as it need not be valid
anymore.

CC: [e-mail]
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
Signed-off-by: Jan Kara <[e-mail]>
---
 block/bfq-cgroup.c  | 36 +++++++++++++++++++++++++++++++++---
 block/bfq-iosched.c |  2 +-
 block/bfq-iosched.h |  1 +
 3 files changed, 35 insertions(+), 4 deletions(-)

Patch

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 24a5c5329bcd..00184530c644 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -729,9 +729,39 @@  static struct bfq_group *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
 	}
 
 	if (sync_bfqq) {
-		entity = &sync_bfqq->entity;
-		if (entity->sched_data != &bfqg->sched_data)
-			bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
+		if (!sync_bfqq->new_bfqq && !bfq_bfqq_coop(sync_bfqq)) {
+			/* We are the only user of this bfqq, just move it */
+			if (sync_bfqq->entity.sched_data != &bfqg->sched_data)
+				bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
+		} else {
+			struct bfq_queue *bfqq;
+
+			/*
+			 * The queue was merged to a different queue. Check
+			 * that the merge chain still belongs to the same
+			 * cgroup.
+			 */
+			for (bfqq = sync_bfqq; bfqq; bfqq = bfqq->new_bfqq)
+				if (bfqq->entity.sched_data !=
+				    &bfqg->sched_data)
+					break;
+			if (bfqq) {
+				/*
+				 * Some queue changed cgroup so the merge is
+				 * not valid anymore. We cannot easily just
+				 * cancel the merge (by clearing new_bfqq) as
+				 * there may be other processes using this
+				 * queue and holding refs to all queues below
+				 * sync_bfqq->new_bfqq. Similarly if the merge
+				 * already happened, we need to detach from
+				 * bfqq now so that we cannot merge bio to a
+				 * request from the old cgroup.
+				 */
+				bfq_put_cooperator(sync_bfqq);
+				bfq_release_process_ref(bfqd, sync_bfqq);
+				bic_set_bfqq(bic, NULL, 1);
+			}
+		}
 	}
 
 	return bfqg;
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 0da47f2ca781..361d321b012a 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5184,7 +5184,7 @@  static void bfq_put_stable_ref(struct bfq_queue *bfqq)
 	bfq_put_queue(bfqq);
 }
 
-static void bfq_put_cooperator(struct bfq_queue *bfqq)
+void bfq_put_cooperator(struct bfq_queue *bfqq)
 {
 	struct bfq_queue *__bfqq, *next;
 
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index a73488eec8a4..6e250db2138e 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -976,6 +976,7 @@  void bfq_weights_tree_remove(struct bfq_data *bfqd,
 void bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
 		     bool compensate, enum bfqq_expiration reason);
 void bfq_put_queue(struct bfq_queue *bfqq);
+void bfq_put_cooperator(struct bfq_queue *bfqq);
 void bfq_end_wr_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg);
 void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq);
 void bfq_schedule_dispatch(struct bfq_data *bfqd);