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Date: Wed, 7 Jun 2017 17:22:06 +0800
From: Ganesh Mahendran <opensource.ganesh@...il.com>
To: jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com,
bart.vanassche@...disk.com, hch@....de
Cc: linux-scsi@...r.kernel.org,
linux-kernel <linux-kernel@...r.kernel.org>,
Ganesh Mahendran <opensource.ganesh@...il.com>
Subject: Re: [PATCH] scsi_lib: increase {host|target|device}_busy count after
dispatch cmd
Ping~ Willing to hear some feed back :-)
Thanks
2017-06-05 17:37 GMT+08:00 Ganesh Mahendran <opensource.ganesh@...il.com>:
> In android system, when there are lots of threads running. Thread A
> holding *host_busy* count is easily to be preempted, and if at the
> same time, thread B set *host_blocked*, then all other threads will
> be io blocked.
>
> Below the detail:
> 1). Thread A calls scsi_request_fn() and it increases *host_busy*.
> But soon it is preempted.
> 2). Thread B call scsi_request_fn(), and it got failure from
> scsi_dispatch_cmd(). So it set *host_blocked*
> 3). All the io blocked...
> 4). Thread A is scheduled again, and it decreases *host_busy*
> in scsi_device_unbusy()
>
> Afer step 2), all the io will be blocked, since scsi_host_queue_ready()
> will always return 0.
> ----
> scsi_host_queue_ready
> {
> if (atomic_read(&shost->host_blocked) > 0) {
> if (busy) ==> true after step 2
> goto starved;
> }
> ----
>
> The system will be unblocked after step 4).
>
> This patch increases {host|target|device}_busy count after dispatch cmd.
>
> Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
> ---
> drivers/scsi/scsi_lib.c | 66 ++++++++++++++++++++++++-------------------------
> 1 file changed, 32 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 884aaa8..9cac272 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -311,6 +311,16 @@ static void scsi_init_cmd_errh(struct scsi_cmnd *cmd)
> cmd->cmd_len = scsi_command_size(cmd->cmnd);
> }
>
> +static void scsi_device_busy(struct scsi_device *sdev)
> +{
> + struct Scsi_Host *shost = sdev->host;
> + struct scsi_target *starget = scsi_target(sdev);
> +
> + atomic_inc(&sdev->device_busy);
> + atomic_inc(&shost->host_busy);
> + atomic_inc(&starget->target_busy);
> +}
> +
> void scsi_device_unbusy(struct scsi_device *sdev)
> {
> struct Scsi_Host *shost = sdev->host;
> @@ -1352,12 +1362,13 @@ static void scsi_unprep_fn(struct request_queue *q, struct request *req)
> static inline int scsi_dev_queue_ready(struct request_queue *q,
> struct scsi_device *sdev)
> {
> + int ret = 0;
> unsigned int busy;
>
> - busy = atomic_inc_return(&sdev->device_busy) - 1;
> + busy = atomic_read(&sdev->device_busy);
> if (atomic_read(&sdev->device_blocked)) {
> if (busy)
> - goto out_dec;
> + goto out;
>
> /*
> * unblock after device_blocked iterates to zero
> @@ -1368,19 +1379,18 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
> */
> if (!q->mq_ops)
> blk_delay_queue(q, SCSI_QUEUE_DELAY);
> - goto out_dec;
> + goto out;
> }
> SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
> "unblocking device at zero depth\n"));
> }
>
> if (busy >= sdev->queue_depth)
> - goto out_dec;
> + goto out;
>
> - return 1;
> -out_dec:
> - atomic_dec(&sdev->device_busy);
> - return 0;
> + ret = 1;
> +out:
> + return ret;
> }
>
> /*
> @@ -1407,7 +1417,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
> if (starget->can_queue <= 0)
> return 1;
>
> - busy = atomic_inc_return(&starget->target_busy) - 1;
> + busy = atomic_read(&starget->target_busy);
> if (atomic_read(&starget->target_blocked) > 0) {
> if (busy)
> goto starved;
> @@ -1416,7 +1426,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
> * unblock after target_blocked iterates to zero
> */
> if (atomic_dec_return(&starget->target_blocked) > 0)
> - goto out_dec;
> + goto out;
>
> SCSI_LOG_MLQUEUE(3, starget_printk(KERN_INFO, starget,
> "unblocking target at zero depth\n"));
> @@ -1431,9 +1441,7 @@ static inline int scsi_target_queue_ready(struct Scsi_Host *shost,
> spin_lock_irq(shost->host_lock);
> list_move_tail(&sdev->starved_entry, &shost->starved_list);
> spin_unlock_irq(shost->host_lock);
> -out_dec:
> - if (starget->can_queue > 0)
> - atomic_dec(&starget->target_busy);
> +out:
> return 0;
> }
>
> @@ -1451,7 +1459,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
> if (scsi_host_in_recovery(shost))
> return 0;
>
> - busy = atomic_inc_return(&shost->host_busy) - 1;
> + busy = atomic_read(&shost->host_busy);
> if (atomic_read(&shost->host_blocked) > 0) {
> if (busy)
> goto starved;
> @@ -1460,7 +1468,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
> * unblock after host_blocked iterates to zero
> */
> if (atomic_dec_return(&shost->host_blocked) > 0)
> - goto out_dec;
> + goto out;
>
> SCSI_LOG_MLQUEUE(3,
> shost_printk(KERN_INFO, shost,
> @@ -1487,8 +1495,7 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
> if (list_empty(&sdev->starved_entry))
> list_add_tail(&sdev->starved_entry, &shost->starved_list);
> spin_unlock_irq(shost->host_lock);
> -out_dec:
> - atomic_dec(&shost->host_busy);
> +out:
> return 0;
> }
>
> @@ -1781,7 +1788,7 @@ static void scsi_request_fn(struct request_queue *q)
> goto not_ready;
>
> if (!scsi_host_queue_ready(q, shost, sdev))
> - goto host_not_ready;
> + goto not_ready;
>
> if (sdev->simple_tags)
> cmd->flags |= SCMD_TAGGED;
> @@ -1800,18 +1807,16 @@ static void scsi_request_fn(struct request_queue *q)
> cmd->scsi_done = scsi_done;
> rtn = scsi_dispatch_cmd(cmd);
> if (rtn) {
> - scsi_queue_insert(cmd, rtn);
> + __scsi_queue_insert(cmd, rtn, 0);
> spin_lock_irq(q->queue_lock);
> goto out_delay;
> }
> + scsi_device_busy(sdev);
> spin_lock_irq(q->queue_lock);
> }
>
> return;
>
> - host_not_ready:
> - if (scsi_target(sdev)->can_queue > 0)
> - atomic_dec(&scsi_target(sdev)->target_busy);
> not_ready:
> /*
> * lock q, handle tag, requeue req, and decrement device_busy. We
> @@ -1823,7 +1828,6 @@ static void scsi_request_fn(struct request_queue *q)
> */
> spin_lock_irq(q->queue_lock);
> blk_requeue_request(q, req);
> - atomic_dec(&sdev->device_busy);
> out_delay:
> if (!atomic_read(&sdev->device_busy) && !scsi_device_blocked(sdev))
> blk_delay_queue(q, SCSI_QUEUE_DELAY);
> @@ -1931,14 +1935,14 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
> if (!scsi_dev_queue_ready(q, sdev))
> goto out_put_device;
> if (!scsi_target_queue_ready(shost, sdev))
> - goto out_dec_device_busy;
> + goto out_put_device;
> if (!scsi_host_queue_ready(q, shost, sdev))
> - goto out_dec_target_busy;
> + goto out_put_device;
>
> if (!(req->rq_flags & RQF_DONTPREP)) {
> ret = prep_to_mq(scsi_mq_prep_fn(req));
> if (ret != BLK_MQ_RQ_QUEUE_OK)
> - goto out_dec_host_busy;
> + goto out_put_device;
> req->rq_flags |= RQF_DONTPREP;
> } else {
> blk_mq_start_request(req);
> @@ -1956,18 +1960,12 @@ static int scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
> if (reason) {
> scsi_set_blocked(cmd, reason);
> ret = BLK_MQ_RQ_QUEUE_BUSY;
> - goto out_dec_host_busy;
> + goto out_put_device;
> }
> + scsi_device_busy(sdev);
>
> return BLK_MQ_RQ_QUEUE_OK;
>
> -out_dec_host_busy:
> - atomic_dec(&shost->host_busy);
> -out_dec_target_busy:
> - if (scsi_target(sdev)->can_queue > 0)
> - atomic_dec(&scsi_target(sdev)->target_busy);
> -out_dec_device_busy:
> - atomic_dec(&sdev->device_busy);
> out_put_device:
> put_device(&sdev->sdev_gendev);
> out:
> --
> 1.9.1
>
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