Re: [PATCH v2] mmc: inline the first mmc_scan() on mmc_start_host()

[Ulf Hansson <ulf.hansson@linaro.org>]

On Tue, 27 Jun 2023 at 19:20, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> Hi Dennis,
>
> On Thu, Mar 30, 2023 at 1:48 AM Dennis Zhou <dennis@kernel.org> wrote:
> > When using dm-verity with a data partition on an emmc device, dm-verity
> > races with the discovery of attached emmc devices. This is because mmc's
> > probing code sets up the host data structure then a work item is
> > scheduled to do discovery afterwards. To prevent this race on init,
> > let's inline the first call to detection, __mm_scan(), and let
> > subsequent detect calls be handled via the workqueue.
> >
> > Signed-off-by: Dennis Zhou <dennis@kernel.org>
>
> Thanks for your patch, which is now commit 2cc83bf7d41113d9 ("mmc:
> core: Allow mmc_start_host() synchronously detect a card") in
> linux-next/master mmc/next next-20230614 next-20230615 next-20230616
>
> I have bisected the following failure on Renesas Salvator-XS with R-Car H3
> ES2.0 to the above commit:
>
>     renesas_sdhi_internal_dmac ee140000.mmc: timeout waiting for
> hardware interrupt (CMD0)
>     renesas_sdhi_internal_dmac ee140000.mmc: timeout waiting for
> hardware interrupt (CMD1)
>     renesas_sdhi_internal_dmac ee140000.mmc: timeout waiting for
> hardware interrupt (CMD0)
>     renesas_sdhi_internal_dmac ee140000.mmc: timeout waiting for
> hardware interrupt (CMD1)
>     mmc0: Failed to initialize a non-removable card

Thanks for reporting!

After I had a closer look, I realize that all the renesas/tmio drivers
are suffering from the similar problem. A host driver must not call
mmc_add_host() before it's ready to serve requests.

Things like initializing an irq-handler must be done before
mmc_add_host() is called, which is not the case for renesas/tmio. In
fact, there seems to be a few other host drivers that have the similar
pattern in their probe routines.

Note that, even if the offending commit below triggers this problem
100% of the cases (as the probe path has now becomes synchronous),
there was a potential risk even before. Previously, mmc_add_host()
ended up punting a work - and if that work ended up sending a request
to the host driver, *before* the irq-handler would be ready, we would
hit the similar problem. I bet adding an msleep(1000) immediately
after mmc_add_host() in tmio_mmc_host_probe(), would then trigger this
problem too. :-)

That said, I am going to revert the offending commit to fix these
problems, for now. Then I will try to help out and fixup the relevant
host drivers  - and when that is done, we can give this whole thing a
new try.

Any objections or other suggestions to this?

Kind regards
Uffe

>
> Reverting the commit fixes the issue for me.
>
> > --- a/drivers/mmc/core/core.c
> > +++ b/drivers/mmc/core/core.c
> > @@ -2185,10 +2185,8 @@ int mmc_card_alternative_gpt_sector(struct mmc_card *card, sector_t *gpt_sector)
> >  }
> >  EXPORT_SYMBOL(mmc_card_alternative_gpt_sector);
> >
> > -void mmc_rescan(struct work_struct *work)
> > +static void __mmc_rescan(struct mmc_host *host)
> >  {
> > -       struct mmc_host *host =
> > -               container_of(work, struct mmc_host, detect.work);
> >         int i;
> >
> >         if (host->rescan_disable)
> > @@ -2249,6 +2247,14 @@ void mmc_rescan(struct work_struct *work)
> >                 mmc_schedule_delayed_work(&host->detect, HZ);
> >  }
> >
> > +void mmc_rescan(struct work_struct *work)
> > +{
> > +       struct mmc_host *host =
> > +               container_of(work, struct mmc_host, detect.work);
> > +
> > +       __mmc_rescan(host);
> > +}
> > +
> >  void mmc_start_host(struct mmc_host *host)
> >  {
> >         host->f_init = max(min(freqs[0], host->f_max), host->f_min);
> > @@ -2261,7 +2267,8 @@ void mmc_start_host(struct mmc_host *host)
> >         }
> >
> >         mmc_gpiod_request_cd_irq(host);
> > -       _mmc_detect_change(host, 0, false);
> > +       host->detect_change = 1;
> > +       __mmc_rescan(host);
> >  }
> >
> >  void __mmc_stop_host(struct mmc_host *host)
>
> 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