path: root/block
diff options
authorMing Lei <>2021-08-11 22:26:24 +0800
committerJens Axboe <>2021-08-17 08:33:32 -0600
commitc2da19ed50554ce52ecbad3655c98371fe58599f (patch)
tree38a1fc5da3c8c9127dd717682043dc6ac4bbfeac /block
parentc797b40ccc340b8a66f7a7842aecc90bf749f087 (diff)
blk-mq: fix kernel panic during iterating over flush request
For fixing use-after-free during iterating over requests, we grabbed request's refcount before calling ->fn in commit 2e315dc07df0 ("blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter"). Turns out this way may cause kernel panic when iterating over one flush request: 1) old flush request's tag is just released, and this tag is reused by one new request, but ->rqs[] isn't updated yet 2) the flush request can be re-used for submitting one new flush command, so blk_rq_init() is called at the same time 3) meantime blk_mq_queue_tag_busy_iter() is called, and old flush request is retrieved from ->rqs[tag]; when blk_mq_put_rq_ref() is called, flush_rq->end_io may not be updated yet, so NULL pointer dereference is triggered in blk_mq_put_rq_ref(). Fix the issue by calling refcount_set(&flush_rq->ref, 1) after flush_rq->end_io is set. So far the only other caller of blk_rq_init() is scsi_ioctl_reset() in which the request doesn't enter block IO stack and the request reference count isn't used, so the change is safe. Fixes: 2e315dc07df0 ("blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter") Reported-by: "Blank-Burian, Markus, Dr." <> Tested-by: "Blank-Burian, Markus, Dr." <> Signed-off-by: Ming Lei <> Reviewed-by: Christoph Hellwig <> Reviewed-by: John Garry <> Link: Signed-off-by: Jens Axboe <>
Diffstat (limited to 'block')
2 files changed, 8 insertions, 1 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index 04477697ee4b..4f8449b29b21 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -122,7 +122,6 @@ void blk_rq_init(struct request_queue *q, struct request *rq)
rq->internal_tag = BLK_MQ_NO_TAG;
rq->start_time_ns = ktime_get_ns();
rq->part = NULL;
- refcount_set(&rq->ref, 1);
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 1002f6c58181..4912c8dbb1d8 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -329,6 +329,14 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
flush_rq->rq_flags |= RQF_FLUSH_SEQ;
flush_rq->rq_disk = first_rq->rq_disk;
flush_rq->end_io = flush_end_io;
+ /*
+ * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
+ * implied in refcount_inc_not_zero() called from
+ * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
+ * and READ flush_rq->end_io
+ */
+ smp_wmb();
+ refcount_set(&flush_rq->ref, 1);
blk_flush_queue_rq(flush_rq, false);