Re: [PATCH] mmc: don't request CD IRQ until mmc_start_host()

[Stephen Warren]

On 09/17/2014 01:55 PM, Ulf Hansson wrote:
> On 12 September 2014 19:18, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
> > From: Stephen Warren <swarren@xxxxxxxxxx>
> >
> > As soon as the CD IRQ is requested, it can trigger, since it's an
> > externally controlled event. If it does, delayed_work host->detect will
> > be scheduled.
> >
> > Many host controller probe()s are roughly structured as:
> >
> > *_probe() {
> >      host = sdhci_pltfm_init();
> >      mmc_of_parse(host->mmc);
> >      rc = sdhci_add_host(host);
> >      if (rc) {
> >          sdhci_pltfm_free();
> >          return rc;
> >      }
> >
> > In 3.17, CD IRQs can are enabled quite early via *_probe() ->
> > mmc_of_parse() -> mmc_gpio_request_cd() -> mmc_gpiod_request_cd_irq().
> >
> > Note that in linux-next, mmc_of_parse() calls mmc_gpio*d*_request_cd()
> > rather than mmc_gpio_request_cd(), and mmc_gpio*d*_request_cd() doesn't
> > call mmc_gpiod_request_cd_irq(). However, this issue still exists for
> > any other direct users of mmc_gpio_request_cd().
> >
> > sdhci_add_host() may fail part way through (e.g. due to deferred
> > probe for a vmmc regulator), and sdhci_pltfm_free() does nothing to
> > unrequest the CD IRQ nor cancel the delayed_work. sdhci_pltfm_free() is
> > coded to assume that if sdhci_add_host() failed, then the delayed_work
> > cannot (or should not) have been triggered.
> >
> > This can lead to the following with CONFIG_DEBUG_OBJECTS_* enabled, when
> > kfree(host) is eventually called inside sdhci_pltfm_free():
> >
> > WARNING: CPU: 2 PID: 6 at lib/debugobjects.c:263 debug_print_object+0x8c/0xb4()
> > ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x18
> >
> > The object being complained about is host->detect.
> >
> > There's no need to request the CD IRQ so early; mmc_start_host() already
> > requests it, and I *assume* that mmc_start_host() is called somehow for
> > all host controllers. For SDHCI hosts at least, the typical call path
> > that does this is: *_probe() -> sdhci_add_host() -> mmc_add_host() ->
> > mmc_start_host(). So, remove the call to mmc_gpiod_request_cd_irq() from
> > mmc_gpio_request_cd(). This matches mmc_gpio*d*_request_cd(), which
> > already doesn't call mmc_gpiod_request_cd_irq().
> >
> > This solves the problem (eliminates the kernel error message above),
> > since it guarantees that the IRQ can't trigger before mmc_start_host()
> > is called.
> >
> > The critical point here is that once sdhci_add_host() calls
> > mmc_add_host() -> mmc_start_host(), sdhci_add_host() is coded not to
> > fail. In other words, if there's a chance that mmc_start_host() may have
> > been called, and CD IRQs triggered, and the delayed_work scheduled,
> > sdhci_add_host() won't fail, and so cleanup is no longer via
> > sdhci_pltfm_free() (which doesn't free the IRQ or cancel the work queue)
> > but instead must be via sdhci_remove_host(), which calls mmc_remove_host()
> > -> mmc_stop_host(), which does free the IRQ and cancel the work queue.
> >
> > This fixes what I might conclude to be a mistake in commit 740a221ef0e5
> > ("mmc: slot-gpio: Add GPIO descriptor based CD GPIO API"), which added the
> > call from mmc_start_host() to mmc_gpiod_request_cd_irq(), but also added
> > incorrectly added a call from mmc_gpio_request_cd() to
> > mmc_gpiod_request_cd_irq().
> >
> > CC: Russell King <linux@xxxxxxxxxxxxxxxx>
> > Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> > Cc: Alexandre Courbot <acourbot@xxxxxxxxxx>
> > Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
> > Signed-off-by: Stephen Warren <swarren@xxxxxxxxxx>
>
> Hi Stephen,
>
> Thanks for looking into this. It seems like this issue has been
> present for quite a while.
> I believe your patch should have a stable tag for 3.15+ as well,
> unless you object I will add it.

Yes, that probably makes sense, thanks.
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