On 09/18/2014 12:49 AM, Adrian Hunter wrote:
On 09/18/2014 08:25 AM, 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().
That comment is wrong. mmc_gpio_request_cd() has always set up the irq.
Uggh, yes. I did misinterpret your patch again, so that one paragraph is
just wrong.
Aside from that though, I do think my patch is a step in the correct
direction. It just needs some thought how to avoid the other issue you
mentioned - that some drivers rely on calling mmc_gpio_request_cd()
after the call to mmc_start().
Perhaps the logic should not be to remove mmc_gpio_request_cd()'s call
to mmc_gpiod_request_cd_irq(), but rather to make it conditional upon
mmc_start_host() having already been called; I assume that state that
can easily be checked to determine that.
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