[PATCH AUTOSEL 5.17 17/20] blk-mq: avoid to touch q->elevator without any protection

Sasha Levin
2022-06-21T20:59:44Z

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 4d337cebcb1c27d9b48c48b9a98e939d4552d584 ]

q->elevator is referred in blk_mq_has_sqsched() without any protection,
no .q_usage_counter is held, no queue srcu and rcu read lock is held,
so potential use-after-free may be triggered.

Fix the issue by adding one queue flag for checking if the elevator
uses single queue style dispatch. Meantime the elevator feature flag
of ELEVATOR_F_MQ_AWARE isn't needed any more.

Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220616014401.817001-3-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/bfq-iosched.c | 3 +++
block/blk-mq-sched.c | 1 +
block/blk-mq.c | 18 ++----------------
block/kyber-iosched.c | 3 ++-
block/mq-deadline.c | 3 +++
include/linux/blkdev.h | 4 ++--
6 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 5d2d3fe65a9d..47ee2e592240 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7183,6 +7183,9 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
bfq_init_root_group(bfqd->root_group, bfqd);
bfq_init_entity(&bfqd->oom_bfqq.entity, bfqd->root_group);

+ /* We dispatch from request queue wide instead of hw queue */
+ blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
+
wbt_disable_default(q);
return 0;

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 80e0eb26b697..f50f1facd164 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -563,6 +563,7 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
int ret;

if (!e) {
+ blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
q->elevator = NULL;
q->nr_requests = q->tag_set->queue_depth;
return 0;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5021e8ed2053..8f77023c0f39 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2095,20 +2095,6 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
}
EXPORT_SYMBOL(blk_mq_run_hw_queue);

-/*
- * Is the request queue handled by an IO scheduler that does not respect
- * hardware queues when dispatching?
- */
-static bool blk_mq_has_sqsched(struct request_queue *q)
-{
- struct elevator_queue *e = q->elevator;
-
- if (e && e->type->ops.dispatch_request &&
- !(e->type->elevator_features & ELEVATOR_F_MQ_AWARE))
- return true;
- return false;
-}
-
/*
* Return prefered queue to dispatch from (if any) for non-mq aware IO
* scheduler.
@@ -2141,7 +2127,7 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async)
int i;

sq_hctx = NULL;
- if (blk_mq_has_sqsched(q))
+ if (blk_queue_sq_sched(q))
sq_hctx = blk_mq_get_sq_hctx(q);
queue_for_each_hw_ctx(q, hctx, i) {
if (blk_mq_hctx_stopped(hctx))
@@ -2169,7 +2155,7 @@ void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs)
int i;

sq_hctx = NULL;
- if (blk_mq_has_sqsched(q))
+ if (blk_queue_sq_sched(q))
sq_hctx = blk_mq_get_sq_hctx(q);
queue_for_each_hw_ctx(q, hctx, i) {
if (blk_mq_hctx_stopped(hctx))
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 70ff2a599ef6..8f7c745b4a57 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -421,6 +421,8 @@ static int kyber_init_sched(struct request_queue *q, struct elevator_type *e)

blk_stat_enable_accounting(q);

+ blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
+
eq->elevator_data = kqd;
q->elevator = eq;

@@ -1033,7 +1035,6 @@ static struct elevator_type kyber_sched = {
#endif
.elevator_attrs = kyber_sched_attrs,
.elevator_name = "kyber",
- .elevator_features = ELEVATOR_F_MQ_AWARE,
.elevator_owner = THIS_MODULE,
};

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 6ed602b2f80a..1a9e835e816c 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -642,6 +642,9 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
spin_lock_init(&dd->lock);
spin_lock_init(&dd->zone_lock);

+ /* We dispatch from request queue wide instead of hw queue */
+ blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
+
q->elevator = eq;
return 0;

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 16b47035e4b0..aa4fc2f5defc 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -412,6 +412,7 @@ struct request_queue {
#define QUEUE_FLAG_RQ_ALLOC_TIME 27 /* record rq->alloc_time_ns */
#define QUEUE_FLAG_HCTX_ACTIVE 28 /* at least one blk-mq hctx is active */
#define QUEUE_FLAG_NOWAIT 29 /* device supports NOWAIT */
+#define QUEUE_FLAG_SQ_SCHED 30 /* single queue style io dispatch */

#define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_SAME_COMP) | \
@@ -457,6 +458,7 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
#define blk_queue_fua(q) test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags)
#define blk_queue_registered(q) test_bit(QUEUE_FLAG_REGISTERED, &(q)->queue_flags)
#define blk_queue_nowait(q) test_bit(QUEUE_FLAG_NOWAIT, &(q)->queue_flags)
+#define blk_queue_sq_sched(q) test_bit(QUEUE_FLAG_SQ_SCHED, &(q)->queue_flags)

extern void blk_set_pm_only(struct request_queue *q);
extern void blk_clear_pm_only(struct request_queue *q);
@@ -738,8 +740,6 @@ void disk_set_independent_access_ranges(struct gendisk *disk,
*/
/* Supports zoned block devices sequential write constraint */
#define ELEVATOR_F_ZBD_SEQ_WRITE (1U << 0)
-/* Supports scheduling on multiple hardware queues */
-#define ELEVATOR_F_MQ_AWARE (1U << 1)

extern void blk_queue_required_elevator_features(struct request_queue *q,
unsigned int features);
--
2.35.1