lkml.org 
[lkml]   [2022]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 5.10] block: fix null-deref in percpu_ref_put
Date
From: Zhang Wensheng <zhangwensheng5@huawei.com>

In the use of q_usage_counter of request_queue, blk_cleanup_queue using
"wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter))"
to wait q_usage_counter becoming zero. however, if the q_usage_counter
becoming zero quickly, and percpu_ref_exit will execute and ref->data
will be freed, maybe another process will cause a null-defef problem
like below:

CPU0 CPU1
blk_cleanup_queue
blk_freeze_queue
blk_mq_freeze_queue_wait
scsi_end_request
percpu_ref_get
...
percpu_ref_put
atomic_long_sub_and_test
percpu_ref_exit
ref->data -> NULL
ref->data->release(ref) -> null-deref

Fix it by setting flag(QUEUE_FLAG_USAGE_COUNT_SYNC) to add synchronization
mechanism, when ref->data->release is called, the flag will be setted,
and the "wait_event" in blk_mq_freeze_queue_wait must wait flag becoming
true as well, which will limit percpu_ref_exit to execute ahead of time.

Signed-off-by: Zhang Wensheng <zhangwensheng5@huawei.com>
---
block/blk-core.c | 4 +++-
block/blk-mq.c | 7 +++++++
include/linux/blk-mq.h | 1 +
include/linux/blkdev.h | 2 ++
4 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 26664f2a139e..238d0f3cd279 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -385,7 +385,8 @@ void blk_cleanup_queue(struct request_queue *q)
* prevent that blk_mq_run_hw_queues() accesses the hardware queues
* after draining finished.
*/
- blk_freeze_queue(q);
+ blk_freeze_queue_start(q);
+ blk_mq_freeze_queue_wait_sync(q);

rq_qos_exit(q);

@@ -500,6 +501,7 @@ static void blk_queue_usage_counter_release(struct percpu_ref *ref)
struct request_queue *q =
container_of(ref, struct request_queue, q_usage_counter);

+ blk_queue_flag_set(QUEUE_FLAG_USAGE_COUNT_SYNC, q);
wake_up_all(&q->mq_freeze_wq);
}

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c5d82b21a1cc..15c4e4530c87 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -134,6 +134,7 @@ void blk_freeze_queue_start(struct request_queue *q)
{
mutex_lock(&q->mq_freeze_lock);
if (++q->mq_freeze_depth == 1) {
+ blk_queue_flag_clear(QUEUE_FLAG_USAGE_COUNT_SYNC, q);
percpu_ref_kill(&q->q_usage_counter);
mutex_unlock(&q->mq_freeze_lock);
if (queue_is_mq(q))
@@ -144,6 +145,12 @@ void blk_freeze_queue_start(struct request_queue *q)
}
EXPORT_SYMBOL_GPL(blk_freeze_queue_start);

+void blk_mq_freeze_queue_wait_sync(struct request_queue *q)
+{
+ wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter) &&
+ test_bit(QUEUE_FLAG_USAGE_COUNT_SYNC, &q->queue_flags));
+}
+
void blk_mq_freeze_queue_wait(struct request_queue *q)
{
wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter));
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f8ea27423d1d..95b2c904375f 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -522,6 +522,7 @@ void blk_mq_freeze_queue(struct request_queue *q);
void blk_mq_unfreeze_queue(struct request_queue *q);
void blk_freeze_queue_start(struct request_queue *q);
void blk_mq_freeze_queue_wait(struct request_queue *q);
+void blk_mq_freeze_queue_wait_sync(struct request_queue *q);
int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
unsigned long timeout);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 98fdf5a31fd6..b61461e3a734 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -629,6 +629,8 @@ 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 */
+/* sync for q_usage_counter */
+#define QUEUE_FLAG_USAGE_COUNT_SYNC 30

#define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_SAME_COMP) | \
--
2.31.1
\
 
 \ /
  Last update: 2022-07-29 09:21    [W:0.037 / U:0.324 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site