When the process is migrated to a different cgroup (or in case of
writeback just starts submitting bios associated with a different
cgroup) bfq_merge_bio() can operate with stale cgroup information in
bic. Thus the bio can be merged to a request from a different cgroup or
it can result in merging of bfqqs for different cgroups or bfqqs of
already dead cgroups and causing possible use-after-free issues. Fix the
problem by updating cgroup information in bfq_merge_bio().
CC: stable@xxxxxxxxxxxxxxx
Fixes: e21b7a0b9887 ("block, bfq: add full hierarchical scheduling and cgroups support")
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
block/bfq-cgroup.c | 40 ++++++++++++++++++++++------------------
block/bfq-iosched.c | 11 +++++++++--
2 files changed, 31 insertions(+), 20 deletions(-)
diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index dbc117e00783..f6f5f156b9f2 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -729,30 +729,34 @@ 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) {
+ struct bfq_queue *orig_bfqq = sync_bfqq;
+
+ /* Traverse the merge chain to bfqq we will be using */
+ while (sync_bfqq->new_bfqq)
+ sync_bfqq = sync_bfqq->new_bfqq;
+ /*
+ * Target bfqq got moved to a different cgroup or this process
+ * started submitting bios for different cgroup?
+ */
+ if (sync_bfqq->entity.sched_data != &bfqg->sched_data) {
/*
* Was the queue we use merged to a different queue?
- * Detach process from the queue as merge need not be
- * valid anymore. We cannot easily cancel the merge as
- * there may be other processes scheduled to this
- * queue.
+ * Detach process from the queue as 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.
*/
- if (sync_bfqq->new_bfqq) {
- bfq_put_cooperator(sync_bfqq);
- bfq_release_process_ref(bfqd, sync_bfqq);
+ if (orig_bfqq != sync_bfqq || bfq_bfqq_coop(sync_bfqq)) {
+ bfq_put_cooperator(orig_bfqq);
+ bfq_release_process_ref(bfqd, orig_bfqq);
bic_set_bfqq(bic, NULL, 1);
return bfqg;
}
- /*
- * 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);
- }
+ /* We are the only user of this bfqq, just move it */
bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
}
}
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 361d321b012a..8a088d77a0b6 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2337,10 +2337,17 @@ static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
spin_lock_irq(&bfqd->lock);
- if (bic)
+ if (bic) {
+ /*
+ * Make sure cgroup info is uptodate for current process before
+ * considering the merge.
+ */
+ bfq_bic_update_cgroup(bic, bio);
+
bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
- else
+ } else {
bfqd->bio_bfqq = NULL;
+ }
bfqd->bio_bic = bic;
ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free);
--
2.31.1
