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

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

Hi Bart,

On Wed, Jul 20, 2022 at 6:51 PM Bart Van Assche <bvanassche@acm.org> wrote:
> On 7/20/22 00:47, Geert Uytterhoeven wrote:
> > With more debug options enabled, it prints:
> >
> > INFO: task kworker/0:7:283 blocked for more than 120 seconds.
> >        Not tainted 5.19.0-rc7-salvator-x-00794-g6780eb02b605 #1287
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > task:kworker/0:7     state:D stack:    0 pid:  283 ppid:     2 flags:0x00000008
> > Workqueue: events ata_scsi_dev_rescan
> > Call trace:
> >   __switch_to+0xbc/0x124
> >   __schedule+0x540/0x71c
> >   schedule+0x58/0xa0
> >   io_schedule+0x18/0x34
> >   blk_mq_get_tag+0x138/0x244
> >   __blk_mq_alloc_requests+0x130/0x2f0
> >   blk_mq_alloc_request+0x74/0xa8
> >   scsi_alloc_request+0x10/0x30
> >   __scsi_execute+0x5c/0x18c
> >   scsi_vpd_inquiry+0x7c/0xdc
> >   scsi_get_vpd_size+0x34/0xa8
> >   scsi_get_vpd_buf+0x28/0xf4
> >   scsi_attach_vpd+0x44/0x170
> >   scsi_rescan_device+0x30/0x98
> >   ata_scsi_dev_rescan+0xc8/0xfc
> >   process_one_work+0x2e0/0x474
> >   worker_thread+0x1cc/0x270
> >   kthread+0xd8/0xe8
> >   ret_from_fork+0x10/0x20
> >
> > This doesn't look like it's blocked in the R-Car SATA driver, but on
> > some I/O scheduling event in the block core?
>
> I'm not familiar with the SATA code but from a quick look it seems like
> the above code is only triggered from inside the ATA error handler
> (ata_do_eh() -> ata_eh_recover() -> ata_eh_revalidate_and_attach() ->
> schedule_work(&(ap->scsi_rescan_task) -> ata_scsi_dev_rescan()). It
> doesn't seem normal to me that the ATA error handler gets invoked during
> a resume. How about testing the following two code changes?

Thanks for your suggestions!

> * In sd_start_stop_device(), change "return sd_submit_start(sdkp, cmd,
> sizeof(cmd))" into "sd_submit_start(sdkp, cmd, sizeof(cmd))" and below
> that call add "flush_work(&sdkp->start_done_work)". This makes
> sd_start_stop_device() again synchronous. This will learn us whether the
> behavior change is caused by submitting the START command from another
> context or by not waiting until the START command has finished.

Unfortunately this doesn't have any impact.

> * Back out the above change, change "return sd_submit_start(sdkp, cmd,
> sizeof(cmd))" again into "sd_submit_start(sdkp, cmd, sizeof(cmd))" and
> below that statement add a call to
> scsi_run_queue(sdkp->device->request_queue). If this change helps it

(that's the static scsi_run_queue() in drivers/scsi/scsi_lib.c?)

> means that the scsi_run_queue() call is necessary to prevent reordering
> of the START command with other SCSI commands.

Unfortunately this doesn't have any impact either.

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