Re: [PATCH V7 6/6] SCSI: set block queue at preempt only when SCSI device is put into quiesce
From: Christoph Hellwig
Date: Mon Oct 02 2017 - 09:52:31 EST
> + /*
> + * 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);
> 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)
> + blk_set_preempt_only(sdev->request_queue, false);