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author | Yufen Yu <yuyufen@huawei.com> | 2019-09-27 10:19:55 +0200 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2019-09-27 15:01:25 +0200 |
commit | 8d6996630c03d7ceeabe2611378fea5ca1c3f1b3 (patch) | |
tree | 2663815e5f56768c84d80685d1c4dc44156a9840 /block/blk.h | |
parent | rq-qos: get rid of redundant wbt_update_limits() (diff) | |
download | linux-8d6996630c03d7ceeabe2611378fea5ca1c3f1b3.tar.xz linux-8d6996630c03d7ceeabe2611378fea5ca1c3f1b3.zip |
block: fix null pointer dereference in blk_mq_rq_timed_out()
We got a null pointer deference BUG_ON in blk_mq_rq_timed_out()
as following:
[ 108.825472] BUG: kernel NULL pointer dereference, address: 0000000000000040
[ 108.827059] PGD 0 P4D 0
[ 108.827313] Oops: 0000 [#1] SMP PTI
[ 108.827657] CPU: 6 PID: 198 Comm: kworker/6:1H Not tainted 5.3.0-rc8+ #431
[ 108.829503] Workqueue: kblockd blk_mq_timeout_work
[ 108.829913] RIP: 0010:blk_mq_check_expired+0x258/0x330
[ 108.838191] Call Trace:
[ 108.838406] bt_iter+0x74/0x80
[ 108.838665] blk_mq_queue_tag_busy_iter+0x204/0x450
[ 108.839074] ? __switch_to_asm+0x34/0x70
[ 108.839405] ? blk_mq_stop_hw_queue+0x40/0x40
[ 108.839823] ? blk_mq_stop_hw_queue+0x40/0x40
[ 108.840273] ? syscall_return_via_sysret+0xf/0x7f
[ 108.840732] blk_mq_timeout_work+0x74/0x200
[ 108.841151] process_one_work+0x297/0x680
[ 108.841550] worker_thread+0x29c/0x6f0
[ 108.841926] ? rescuer_thread+0x580/0x580
[ 108.842344] kthread+0x16a/0x1a0
[ 108.842666] ? kthread_flush_work+0x170/0x170
[ 108.843100] ret_from_fork+0x35/0x40
The bug is caused by the race between timeout handle and completion for
flush request.
When timeout handle function blk_mq_rq_timed_out() try to read
'req->q->mq_ops', the 'req' have completed and reinitiated by next
flush request, which would call blk_rq_init() to clear 'req' as 0.
After commit 12f5b93145 ("blk-mq: Remove generation seqeunce"),
normal requests lifetime are protected by refcount. Until 'rq->ref'
drop to zero, the request can really be free. Thus, these requests
cannot been reused before timeout handle finish.
However, flush request has defined .end_io and rq->end_io() is still
called even if 'rq->ref' doesn't drop to zero. After that, the 'flush_rq'
can be reused by the next flush request handle, resulting in null
pointer deference BUG ON.
We fix this problem by covering flush request with 'rq->ref'.
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().
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: stable@vger.kernel.org # v4.18+
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
-------
v2:
- move rq_status from struct request to struct blk_flush_queue
v3:
- remove unnecessary '{}' pair.
v4:
- let spinlock to protect 'fq->rq_status'
v5:
- move rq_status after flush_running_idx member of struct blk_flush_queue
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk.h')
-rw-r--r-- | block/blk.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/block/blk.h b/block/blk.h index 25773d668ec0..47fba9362e60 100644 --- a/block/blk.h +++ b/block/blk.h @@ -19,6 +19,7 @@ struct blk_flush_queue { unsigned int flush_queue_delayed:1; unsigned int flush_pending_idx:1; unsigned int flush_running_idx:1; + blk_status_t rq_status; unsigned long flush_pending_since; struct list_head flush_queue[2]; struct list_head flush_data_in_flight; @@ -47,6 +48,12 @@ 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); |