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

From: Russell King - ARM Linux
Date: Thu Sep 18 2014 - 16:06:54 EST

On Thu, Sep 18, 2014 at 10:39:38AM -0600, Stephen Warren wrote:
> On 09/17/2014 11:25 PM, Adrian Hunter wrote:
>> 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@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.
>> 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 ?
> Oh, if there are drivers that do that, this patch might cause an issue.
> But why are they doing that? Shouldn't all the drivers set up the same
> kinds of resources in the same order and way?

The way this /should/ work is that:

+ mmc_alloc_host() (and corresponding derivatives) should initialise
everything into a safe state.

+ mmc_add_host() (and corresponding derivatives) publishes the host,
and "enables" card discovery etc.

Host drivers should not do anything after mmc_add_host(). Yes, there's
buggy host drivers (particularly the sdhci crap - and even after my
mega patch set, the most friendly and positive term I have to describe
sdhci _is_ "crap") which oops the kernel if you (eg) receive a card
detect IRQ between those two calls, but that's really because the
host driver _is_ crap and not following proper driver initialisation

Someone /really/ needs to sort out MMC and stop this kind of driver
variability poliferating. All drivers should be doing the same thing:

- allocate the host
- map the resources
- claim interrupts etc (it doesn't matter if you schedule the detect
work, mmc_rescan won't process the event if mmc_add_host() hasn't
been called)
- publish the host via mmc_add_host()

Looking through sdhci_add_host(), I notice this:


pr_info("%s: SDHCI controller on %s [%s] using %s\n",
mmc_hostname(mmc), host->hw_name, dev_name(mmc_dev(mmc)),
(host->flags & SDHCI_USE_ADMA) ? "ADMA" :
(host->flags & SDHCI_USE_SDMA) ? "DMA" : "PIO");


return 0;


int mmc_add_host(struct mmc_host *host)
int err;

err = mmc_of_parse_child(host);
if (err)
return err;
err = device_add(&host->class_dev);
if (err)
return err;

Like I say, it's crap...

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