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

[Jan Kara <jack@suse.cz>]

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.

CC: stable@vger.kernel.org
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bfq-cgroup.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 24a5c5329bcd..1f5fb723bed7 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -730,8 +730,18 @@ 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)
+		if (entity->sched_data != &bfqg->sched_data) {
+			/*
+			 * Moving bfqq that is shared with another process?
+			 * Split the queues at the nearest occasion as the
+			 * processes can be in different cgroups now.
+			 */
+			if (bfq_bfqq_coop(sync_bfqq)) {
+				bic->stably_merged = false;
+				bfq_mark_bfqq_split_coop(sync_bfqq);
+			}
 			bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
+		}
 	}
 
 	return bfqg;
-- 
2.26.2