From: Yufen Yu <yuyufen@huawei.com>
To: <axboe@kernel.dk>
Cc: <linux-block@vger.kernel.org>, <hch@infradead.org>,
<keith.busch@intel.com>, <tj@kernel.org>, <yuyufen@huawei.com>,
<zhangxiaoxu5@huawei.com>
Subject: [PATCH] block: fix null pointer dereference in blk_mq_rq_timed_out()
Date: Sat, 7 Sep 2019 18:24:50 +0800 [thread overview]
Message-ID: <20190907102450.40291-1-yuyufen@huawei.com> (raw)
There is a race condition between timeout check and completion for
flush request as follow:
timeout_work issue flush issue flush
blk_insert_flush
blk_insert_flush
blk_mq_timeout_work
blk_kick_flush
blk_mq_queue_tag_busy_iter
blk_mq_check_expired(flush_rq)
__blk_mq_end_request
flush_end_io
blk_kick_flush
blk_rq_init(flush_rq)
memset(flush_rq, 0)
blk_mq_timed_out
BUG_ON flush_rq->q->mq_ops
For normal request, we need to get a tag and then allocate corresponding request.
Thus, the request cannot be reallocated before the tag have been free.
Commit 1d9bd5161ba ("blk-mq: replace timeout synchronization with a RCU and
generation based scheme") and commit 12f5b93145 ("blk-mq: Remove generation
seqeunce") can guarantee the consistency of timeout handle and completion.
However, 'flush_rq' have been forgotten. 'flush_rq' allocation management
dependents on flush implemention mechanism. Each hctx has only one 'flush_rq'.
When a flush request have completed, the next flush request will hold the 'flush_rq'.
In the end, timeout handle may access the cleared 'flush_rq'.
We fix this problem by checking request refcount 'rq->ref', as normal request.
If the refcount is not zero, flush_end_io() return and wait the last holder
recall it. To record the request status, we add a new entry 'rq_status',
which will be used in flush_end_io().
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
---
block/blk-flush.c | 8 ++++++++
block/blk-mq.c | 7 +++++--
block/blk.h | 5 +++++
include/linux/blkdev.h | 2 ++
4 files changed, 20 insertions(+), 2 deletions(-)
diff --git a/block/blk-flush.c b/block/blk-flush.c
index aedd9320e605..359a7e1a0925 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -212,6 +212,14 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
struct blk_mq_hw_ctx *hctx;
+ if (!refcount_dec_and_test(&flush_rq->ref)) {
+ flush_rq->rq_status = error;
+ return;
+ }
+
+ if (flush_rq->rq_status != BLK_STS_OK)
+ error = flush_rq->rq_status;
+
/* release the tag's ownership to the req cloned from */
spin_lock_irqsave(&fq->mq_flush_lock, flags);
hctx = flush_rq->mq_hctx;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0835f4d8d42e..3d2b2c2e9cdf 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -905,9 +905,12 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
*/
if (blk_mq_req_expired(rq, next))
blk_mq_rq_timed_out(rq, reserved);
- if (refcount_dec_and_test(&rq->ref))
- __blk_mq_free_request(rq);
+ if (is_flush_rq(rq, hctx)) {
+ rq->end_io(rq, 0);
+ } else if (refcount_dec_and_test(&rq->ref)) {
+ __blk_mq_free_request(rq);
+ }
return true;
}
diff --git a/block/blk.h b/block/blk.h
index de6b2e146d6e..f503ef9ad3e6 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -47,6 +47,11 @@ static inline void __blk_get_queue(struct request_queue *q)
kobject_get(&q->kobj);
}
+static inline bool
+is_flush_rq(struct request *req, struct blk_mq_hw_ctx *hctx) {
+ return hctx->fq->flush_rq == req;
+}
+
struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
int node, int cmd_size, gfp_t flags);
void blk_free_flush_queue(struct blk_flush_queue *q);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ef375dafb1c..b1d05077e03f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -237,6 +237,8 @@ struct request {
*/
rq_end_io_fn *end_io;
void *end_io_data;
+
+ blk_status_t rq_status;
};
static inline bool blk_op_is_scsi(unsigned int op)
--
2.17.2
next reply other threads:[~2019-09-07 10:04 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-07 10:24 Yufen Yu [this message]
2019-09-12 2:46 ` [PATCH] block: fix null pointer dereference in blk_mq_rq_timed_out() Ming Lei
2019-09-12 3:29 ` Yufen Yu
2019-09-12 4:16 ` Ming Lei
2019-09-12 8:49 ` Yufen Yu
2019-09-12 10:07 ` Ming Lei
2019-09-16 2:40 ` Yufen Yu
2019-09-16 9:27 ` Yufen Yu
2019-09-17 0:50 ` Ming Lei
2019-09-12 8:59 ` Guoqing Jiang
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