Re: [PATCH] ata,scsi: do not issue START STOP UNIT on resume

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Hi Damien,

On Thu, Sep 14, 2023 at 12:08 AM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
> On 9/13/23 19:34, Geert Uytterhoeven wrote:
> > On Wed, Sep 13, 2023 at 12:21 PM Geert Uytterhoeven
> > <geert@xxxxxxxxxxxxxx> wrote:
> >> On Wed, Sep 13, 2023 at 12:58 AM Damien Le Moal <dlemoal@xxxxxxxxxx> wrote:
> >>> On 9/13/23 02:39, Geert Uytterhoeven wrote:
> >>>> On Mon, 31 Jul 2023, Damien Le Moal wrote:
> >>>>> During system resume, ata_port_pm_resume() triggers ata EH to
> >>>>> 1) Resume the controller
> >>>>> 2) Reset and rescan the ports
> >>>>> 3) Revalidate devices
> >>>>> This EH execution is started asynchronously from ata_port_pm_resume(),
> >>>>> which means that when sd_resume() is executed, none or only part of the
> >>>>> above processing may have been executed. However, sd_resume() issues a
> >>>>> START STOP UNIT to wake up the drive from sleep mode. This command is
> >>>>> translated to ATA with ata_scsi_start_stop_xlat() and issued to the
> >>>>> device. However, depending on the state of execution of the EH process
> >>>>> and revalidation triggerred by ata_port_pm_resume(), two things may
> >>>>> happen:
> >>>>> 1) The START STOP UNIT fails if it is received before the controller has
> >>>>>   been reenabled at the beginning of the EH execution. This is visible
> >>>>>   with error messages like:
> >>>>>
> >>>>> ata10.00: device reported invalid CHS sector 0
> >>>>> sd 9:0:0:0: [sdc] Start/Stop Unit failed: Result: hostbyte=DID_OK driverbyte=DRIVER_OK
> >>>>> sd 9:0:0:0: [sdc] Sense Key : Illegal Request [current]
> >>>>> sd 9:0:0:0: [sdc] Add. Sense: Unaligned write command
> >>>>> sd 9:0:0:0: PM: dpm_run_callback(): scsi_bus_resume+0x0/0x90 returns -5
> >>>>> sd 9:0:0:0: PM: failed to resume async: error -5
> >>>>>
> >>>>> 2) The START STOP UNIT command is received while the EH process is
> >>>>>   on-going, which mean that it is stopped and must wait for its
> >>>>>   completion, at which point the command is rather useless as the drive
> >>>>>   is already fully spun up already. This case results also in a
> >>>>>   significant delay in sd_resume() which is observable by users as
> >>>>>   the entire system resume completion is delayed.
> >>>>>
> >>>>> Given that ATA devices will be woken up by libata activity on resume,
> >>>>> sd_resume() has no need to issue a START STOP UNIT command, which solves
> >>>>> the above mentioned problems. Do not issue this command by introducing
> >>>>> the new scsi_device flag no_start_on_resume and setting this flag to 1
> >>>>> in ata_scsi_dev_config(). sd_resume() is modified to issue a START STOP
> >>>>> UNIT command only if this flag is not set.
> >>>>>
> >>>>> Reported-by: Paul Ausbeck <paula@xxxxxxxxxxxx>
> >>>>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=215880
> >>>>> Fixes: a19a93e4c6a9 ("scsi: core: pm: Rely on the device driver core for async power management")
> >>>>> Signed-off-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
> >>>>
> >>>> Thanks for your patch, which is now commit 0a8589055936d8fe
> >>>> ("ata,scsi: do not issue START STOP UNIT on resume") in v6.5-rc5.
> >>>> Sorry for being late to the party, but this commit landed upstream
> >>>> during my summer holidays, and apparently I wasn't that focussed on
> >>>> noticing small behavioral changes after getting back to work...
> >>>>
> >>>> I noticed an oddity after s2idle or s2ram on Renesas Salvator-XS (R-Car
> >>>> H3 ES2.0) with an old (spinning rust) SATA drive, and bisected it to
> >>>> this commit: when accessing the drive after system resume, there is now
> >>>> a delay of ca. 5s before data is returned, presumably due to starting
> >>>> the drive, and having to wait for it to spin up to be able to read data.
> >>>> But the good news is that the actual system resume takes less time than
> >>>> before (reduced by even more than ca. 5s!), so this looks like a net
> >>>> win...
> >>>
> >>> Thanks for the report. The delay for the first data access from user space right
> >>> after resume is 100% expected, with or without this patch. The reason is that
> >>> waking up the drive (spinning it up) is done asynchronously from the PM resume
> >>> context, so when you get "PM suspend exit" message signaling that the system is
> >>> resumed, the drive may not yet be spinning. Any access will wait for that to
> >>> happen before proceeding. Depending on the drive that can take up to 10s or so.
> >>
> >> That does not match with what I am seeing: before this patch, there
> >> was no delay on first data access from user space, as the drive is fully
> >> spun up when system resume returns.
> >> With this patch, system resume returns earlier, and the drive is only
> >> spun up when user space starts accessing data.
> >>
> >> Note that I do not have any file system mounted, and use
> >> "hd /dev/sda | head -70" to access the disk.
> >>
> >>> I am not entirely sure where the net win you see come from. But the patch you
> >>> mention is in fact completely wrong and does not fix the underlying issues with
> >>> ata suspend/resume and potential deadlocks in PM due to ata ports relationship
> >>> with scsi devices. So I have been working on fixing this for the last 2 weeks,
> >>> after another user also reported issues with the patch you mention [1].
> >>>
> >>> Could you try libata for-next branch on your system ? There are 7 fix patches in
> >>> there that I plan to send out for 6.6-rc2 to fix the patch in question and other
> >>> issues potentially causing deadlocks on resume. The patches were posted also [2].
> >>>
> >>> https://lore.kernel.org/linux-ide/20230912005655.368075-1-dlemoal@xxxxxxxxxx/T/#t
> >>
> >> Unfortunately that didn't work, as /dev/sda no longer exists.
> >> Will reply to the patch I bisected the issue to...
> >
> > With libata/for-next (fa2259a59966c005 ("ata: libata: Cleanup inline
> > DMA helper functions")) and commit 99626085d036ec32 ("ata: libata-scsi:
> > link ata port and scsi device") reverted, it behaves as before (disk
> > is spun up when system resume completes, no delay when accessing the
> > disk from userspace).
>
> I will check the ata platform driver for R-CAR. I may have overlooked something
> in that area. I tested with AHCI and libsas adapters only as I do not have ATA
> on the few ARM SBC boards I have. And I do not have an R-CAR board.
>
> What surprises me is that you need to revert ata: libata: Cleanup inline DMA
> helper functions". This patch has 0 functional changes and really is only a code
> cleanup... Nothing should change with it. Can you confirm that you really need
> to revert that patch to get things working again ?

My apologies, I should have written:

    With libata/for-next (which is currently at fa2259a59966c005 ("ata:
    libata: Cleanup inline DMA helper functions")), and commit
    99626085d036ec32 ("ata: libata-scsi: link ata port and scsi device")
    reverted, ...

So 99626085d036ec32 was the only commit I had to revert.
Sorry for the confusion.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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



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