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

From: Stephen Warren
Date: Wed Sep 17 2014 - 16:05:27 EST

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();
rc = sdhci_add_host(host);
if (rc) {
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

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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