[PATCH] block: re-introduce blk_mq_complete_request_sync

[Ming Lei]

On Thu, Oct 08, 2020 at 02:37:50PM -0700, Sagi Grimberg wrote:
> In nvme-tcp and nvme-rdma, the timeout handler in certain conditions
> needs to complete an aborted request. The timeout handler serializes
> against an error recovery sequence that iterates over the inflight
> requests and cancels them.
> 
> However, the fact that blk_mq_complete_request may defer to a different
> core that serialization breaks.
> 
> Hence re-introduce blk_mq_complete_request_sync and use that in the
> timeout handler to make sure that we don't get a use-after-free
> condition.
> 
> This was uncovered by the blktests:
> --
> $ nvme_trtype=tcp ./check nvme/012
> 
> [ 2152.546343] run blktests nvme/012 at 2020-10-08 05:59:03
> [ 2152.799640] loop: module loaded
> [ 2152.835222] nvmet: adding nsid 1 to subsystem blktests-subsystem-1
> [ 2152.860697] nvmet_tcp: enabling port 0 (127.0.0.1:4420)
> [ 2152.937889] nvmet: creating controller 1 for subsystem blktests-subsystem-1 for NQN nqn.2014-08.org.nvmexpress:uuid:e544149126a24145abeeb6129b0ec52c.
> [ 2152.952085] nvme nvme0: creating 12 I/O queues.
> [ 2152.958042] nvme nvme0: mapped 12/0/0 default/read/poll queues.
> [ 2152.969948] nvme nvme0: new ctrl: NQN "blktests-subsystem-1", addr 127.0.0.1:4420
> [ 2154.927953] XFS (nvme0n1): Mounting V5 Filesystem
> [ 2154.942432] XFS (nvme0n1): Ending clean mount
> [ 2154.948183] xfs filesystem being mounted at /mnt/blktests supports timestamps until 2038 (0x7fffffff)
> [ 2215.193645] nvme nvme0: queue 7: timeout request 0x11 type 4
> [ 2215.199331] nvme nvme0: starting error recovery
> [ 2215.203890] nvme nvme0: queue 7: timeout request 0x12 type 4
> [ 2215.204483] block nvme0n1: no usable path - requeuing I/O
> [ 2215.214976] block nvme0n1: no usable path - requeuing I/O
> [ 2215.215495] nvme nvme0: Reconnecting in 10 seconds...
> [ 2215.215502] ------------[ cut here ]------------
> [ 2215.215505] refcount_t: underflow; use-after-free.
> [ 2215.215617] WARNING: CPU: 6 PID: 45 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
> [ 2215.215745] RSP: 0018:ffffb71b80837dc8 EFLAGS: 00010292
> [ 2215.215750] RAX: 0000000000000026 RBX: 0000000000000000 RCX: ffff93f37dcd8d08
> [ 2215.215753] RDX: 00000000ffffffd8 RSI: 0000000000000027 RDI: ffff93f37dcd8d00
> [ 2215.215755] RBP: ffff93f37a812400 R08: 00000203c5221fce R09: ffffffffa7fffbc4
> [ 2215.215758] R10: 0000000000000477 R11: 000000000002835c R12: ffff93f37a8124e8
> [ 2215.215761] R13: ffff93f37a2b0000 R14: ffffb71b80837e70 R15: ffff93f37a2b0000
> [ 2215.215765] FS:  0000000000000000(0000) GS:ffff93f37dcc0000(0000) knlGS:0000000000000000
> [ 2215.215768] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 2215.215771] CR2: 00005637b4137028 CR3: 000000007c1be000 CR4: 00000000000006e0
> [ 2215.215773] Call Trace:
> [ 2215.215784]  blk_mq_check_expired+0x109/0x1b0
> [ 2215.215797]  blk_mq_queue_tag_busy_iter+0x1b8/0x330
> [ 2215.215801]  ? blk_poll+0x300/0x300
> [ 2215.215806]  blk_mq_timeout_work+0x44/0xe0
> [ 2215.215814]  process_one_work+0x1b4/0x370
> [ 2215.215820]  worker_thread+0x53/0x3e0
> [ 2215.215825]  ? process_one_work+0x370/0x370
> [ 2215.215829]  kthread+0x11b/0x140
> [ 2215.215834]  ? __kthread_bind_mask+0x60/0x60
> [ 2215.215841]  ret_from_fork+0x22/0x30
> [ 2215.215847] ---[ end trace 7d137e36e23c0d19 ]---
> --
> 
> Reported-by: Yi Zhang <yi.zhang at redhat.com>
> Fixes: 236187c4ed19 ("nvme-tcp: fix timeout handler")
> Fixes: 0475a8dcbcee ("nvme-rdma: fix timeout handler")
> Signed-off-by: Sagi Grimberg <sagi at grimberg.me>
> ---
> Yi, would appreciate your Tested-by tag
> 
>  block/blk-mq.c           | 7 +++++++
>  drivers/nvme/host/rdma.c | 2 +-
>  drivers/nvme/host/tcp.c  | 2 +-
>  include/linux/blk-mq.h   | 1 +
>  4 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f8e1e759c905..2d154722ef39 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -729,6 +729,13 @@ bool blk_mq_complete_request_remote(struct request *rq)
>  }
>  EXPORT_SYMBOL_GPL(blk_mq_complete_request_remote);
>  
> +void blk_mq_complete_request_sync(struct request *rq)
> +{
> +	WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
> +	rq->q->mq_ops->complete(rq);
> +}
> +EXPORT_SYMBOL_GPL(blk_mq_complete_request_sync);
> +
>  /**
>   * blk_mq_complete_request - end I/O on a request
>   * @rq:		the request being processed
> diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
> index 9e378d0a0c01..45fc605349da 100644
> --- a/drivers/nvme/host/rdma.c
> +++ b/drivers/nvme/host/rdma.c
> @@ -1975,7 +1975,7 @@ static void nvme_rdma_complete_timed_out(struct request *rq)
>  	nvme_rdma_stop_queue(queue);
>  	if (!blk_mq_request_completed(rq)) {
>  		nvme_req(rq)->status = NVME_SC_HOST_ABORTED_CMD;
> -		blk_mq_complete_request(rq);
> +		blk_mq_complete_request_sync(rq);
>  	}
>  	mutex_unlock(&ctrl->teardown_lock);
>  }
> diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
> index 8f4f29f18b8c..629b025685d1 100644
> --- a/drivers/nvme/host/tcp.c
> +++ b/drivers/nvme/host/tcp.c
> @@ -2177,7 +2177,7 @@ static void nvme_tcp_complete_timed_out(struct request *rq)
>  	nvme_tcp_stop_queue(ctrl, nvme_tcp_queue_id(req->queue));
>  	if (!blk_mq_request_completed(rq)) {
>  		nvme_req(rq)->status = NVME_SC_HOST_ABORTED_CMD;
> -		blk_mq_complete_request(rq);
> +		blk_mq_complete_request_sync(rq);

Or complete the request in the following way? Then one block layer API
can be saved:

	blk_mq_complete_request_remote(rq);
	nvme_complete_rq(rq);


thanks,
Ming