Re: [PATCH v2 2/2] scsi: sd: Rework asynchronous resume support

From: Bart Van Assche <bvanassche@acm.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Martin K . Petersen" <martin.petersen@oracle.com>,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	scsi <linux-scsi@vger.kernel.org>, Ming Lei <ming.lei@redhat.com>,
	Hannes Reinecke <hare@suse.de>,
	John Garry <john.garry@huawei.com>,
	ericspero@icloud.com, jason600.groome@gmail.com,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] scsi: sd: Rework asynchronous resume support
Date: Fri, 22 Jul 2022 10:56:09 -0700	[thread overview]
Message-ID: <084e7c5a-f98d-d61e-de81-83525851ecf9@acm.org> (raw)
In-Reply-To: <CAMuHMdURQpAEGgv4cY7v0rqzs12v2TT=Amt26Y0OoBSW7YAoaw@mail.gmail.com>

On 7/22/22 01:53, Geert Uytterhoeven wrote:
> During s2idle, the following trace data is generated:
> 
>     kworker/u16:9-325     [000] ...2.   230.478731: block_rq_issue: 8,0
> N 0 () 0 + 0 [kworker/u16:9]
>     kworker/u16:9-325     [000] ...2.   230.478745:
> scsi_dispatch_cmd_start: host_no=0 channel=0 id=0 lun=0 data_sgl=0
> prot_sgl=0 prot_op=SCSI_PROT_NORMAL driver_tag=0 scheduler_tag=0
> cmnd=(SYNCHRONIZE_CACHE - raw=35 00 00 00 00 00 00 00 00 00)
>            <idle>-0       [007] d.h3.   230.478832:
> scsi_dispatch_cmd_done: host_no=0 channel=0 id=0 lun=0 data_sgl=0
> prot_sgl=0 prot_op=SCSI_PROT_NORMAL driver_tag=0 scheduler_tag=0
> cmnd=(SYNCHRONIZE_CACHE - raw=35 00 00 00 00 00 00 00 00 00)
> result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE
> status=SAM_STAT_GOOD)
>            <idle>-0       [000] ..s2.   230.478851: block_rq_complete:
> 8,0 N () 18446744073709551615 + 0 [0]
>     kworker/u16:9-325     [000] ...2.   230.483134: block_rq_issue: 8,0
> N 0 () 0 + 0 [kworker/u16:9]
>     kworker/u16:9-325     [000] ...2.   230.483136:
> scsi_dispatch_cmd_start: host_no=0 channel=0 id=0 lun=0 data_sgl=0
> prot_sgl=0 prot_op=SCSI_PROT_NORMAL driver_tag=0 scheduler_tag=1
> cmnd=(START_STOP - raw=1b 00 00 00 00 00)
>            <idle>-0       [007] d.h3.   230.624530:
> scsi_dispatch_cmd_done: host_no=0 channel=0 id=0 lun=0 data_sgl=0
> prot_sgl=0 prot_op=SCSI_PROT_NORMAL driver_tag=0 scheduler_tag=1
> cmnd=(START_STOP - raw=1b 00 00 00 00 00) result=(driver=DRIVER_OK
> host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
>            <idle>-0       [000] d.s4.   230.624634: scsi_eh_wakeup: host_no=0
>            <idle>-0       [000] ..s2.   230.624642: block_rq_complete:
> 8,0 N () 18446744073709551615 + 0 [0]
>    kworker/u16:14-1027    [007] d..3.   231.393642: scsi_eh_wakeup: host_no=0
> 
> When reading from hard drive after s2idle, no more trace data
> is generated.

I think the above commands come from the suspend sequence. '1b 00 00 00 
00 00' stops a block device. The lowest bit in byte 4 needs to be set to 
start a block device.

Something that is not yet clear is whether or not sd_submit_start() 
hangs during the resume process. How about verifying whether or not 
sd_submit_start() hangs by either issuing SysRq-t or by adding pr_info() 
statements in that function?

Thanks,

Bart.