Re: [PATCH V7 6/6] SCSI: set block queue at preempt only when SCSI device is put into quiesce

Christoph Hellwig
2017-10-02T13:52:28Z

> + /*
> + * Simply quiesing SCSI device isn't safe, it is easy
> + * to use up requests because all these allocated requests
> + * can't be dispatched when device is put in QIUESCE.
> + * Then no request can be allocated and we may hang
> + * somewhere, such as system suspend/resume.
> + *
> + * So we set block queue in preempt only first, no new
> + * normal request can enter queue any more, and all pending
> + * requests are drained once blk_set_preempt_only()
> + * returns. Only RQF_PREEMPT is allowed in preempt only mode.
> + */
> + blk_set_preempt_only(sdev->request_queue, true);
> +
> mutex_lock(&sdev->state_mutex);
> err = scsi_device_set_state(sdev, SDEV_QUIESCE);

Why is this not under state_mutex so that we guarantee it's atomic
vs sdev state changes?

> @@ -2964,6 +2981,8 @@ void scsi_device_resume(struct scsi_device *sdev)
> scsi_device_set_state(sdev, SDEV_RUNNING) == 0)
> scsi_run_queue(sdev->request_queue);
> mutex_unlock(&sdev->state_mutex);
> +
> + blk_set_preempt_only(sdev->request_queue, false);

Same here.