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

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hoi Bart,

On Thu, Jul 21, 2022 at 8:15 PM Bart Van Assche <bvanassche@acm.org> wrote:
> On 7/21/22 01:07, Geert Uytterhoeven wrote:
> > On Wed, Jul 20, 2022 at 8:04 PM Bart Van Assche <bvanassche@acm.org> wrote:
> >> That's surprising. Is there anything unusual about the test setup that I
> >> should know, e.g. very small number of CPU cores or a very small queue
> >> depth of the SATA device? How about adding pr_info() statements at the
> >> start and end of the following functions and also before the return
> >> statements in these functions to determine where execution of the START
> >> command hangs?
> >> * sd_start_done().
> >> * sd_start_done_work().
> >
> > None of these functions seem to be called at all?
>
> That's weird. This means that either sd_submit_start() hangs or that the
> execution of the START command never finishes. The latter is unlikely
> since the SCSI error handler is assumed to abort commands that hang. It
> would also be weird if sd_submit_start() would hang before the START
> command is submitted since the code flow for submitting the START
> command is very similar to the code flow for submitting the START
> command without patch "scsi: sd: Rework asynchronous resume support"
> (calling scsi_execute()).

I think you misunderstood: none of these functions seem to be called,
even when reading from hard drive works fine.

> What is also weird is that there are at least two SATA setups on which
> this code works fine, including my Qemu setup.
>
> Although it is possible to enable tracing at boot time, adding the
> following parameters to the kernel command line would generate too much
> logging data:
>
> tp_printk
> trace_event=block_rq_complete,block_rq_error,block_rq_insert,block_rq_issue,block_rq_merge,block_rq_remap,block_rq_requeue,scsi_dispatch_cmd_done,scsi_dispatch_cmd_start,scsi_eh_wakeup,scsi_dispatch_cmd_error,scsi_dispatch_cmd_timeout
> scsi_mod.scsi_logging_level=32256
>
> I'm not sure what the best way is to proceed since I cannot reproduce
> this issue.

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.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds