Date:	Thu, 18 Sep 2014 08:25:01 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Stephen Warren <swarren@...dotorg.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
CC:	Chris Ball <chris@...ntf.net>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stephen Warren <swarren@...dia.com>,
	Russell King <linux@....linux.org.uk>,
	Alexandre Courbot <acourbot@...dia.com>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] mmc: don't request CD IRQ until mmc_start_host()

On 09/17/2014 10:57 PM, Stephen Warren wrote:
> On 09/17/2014 01:55 PM, Ulf Hansson wrote:
>> On 12 September 2014 19:18, Stephen Warren <swarren@...dotorg.org> wrote:
>>> From: Stephen Warren <swarren@...dia.com>
>>>
>>> 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@....linux.org.uk>
>>> Cc: Adrian Hunter <adrian.hunter@...el.com>
>>> Cc: Alexandre Courbot <acourbot@...dia.com>
>>> Cc: Linus Walleij <linus.walleij@...aro.org>
>>> Signed-off-by: Stephen Warren <swarren@...dia.com>
>>
>> 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.

Doesn't this patch break the drivers that call mmc_gpio_request_cd() after
mmc_add_host() like mmc_spi.c or sdhci-sirf.c or tmio_mmc_pio.c ?

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