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

From: Stephen Warren
Date: Mon Sep 22 2014 - 11:57:29 EST

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 if
mmc_gpio_request_cd() is called directly before mmc_start_host().

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. For most SDHCI hosts at least, the typical call path that
does this is: *_probe() -> sdhci_add_host() -> mmc_add_host() ->
mmc_start_host(). Therefore, remove the call to mmc_gpiod_request_cd_irq()
from mmc_gpio_request_cd(). This also matches mmc_gpio*d*_request_cd(),
which already doesn't call mmc_gpiod_request_cd_irq().

However, some host controller drivers call mmc_gpio_request_cd() after
mmc_start_host() has already been called, and assume that this will also
call mmc_gpiod_request_cd_irq(). Update those drivers to explicitly call
mmc_gpiod_request_cd_irq() themselves. Ideally, these drivers should be
modified to move their call to mmc_gpio_request_cd() before their call
to mmc_add_host(). However that's too large a change for stable.

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.

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>
Note: This is a patch for v3.17 (and perhaps earlier); linux-next doesn't
have this problem due to other code re-structing. However, I think those
patches are too large to backport.

v3: Explicitly call mmc_gpiod_request_cd_irq() from drivers that call
mmc_gpio_request_cd() after calling mmc_add_host(), rather than modifying
the function signature of mmc_gpio_request_cd().

v2: Rather than completely removing mmc_gpio_request_cd()'s call to
mmc_gpiod_request_cd_irq(), make the call conditional.
drivers/mmc/core/slot-gpio.c | 2 --
drivers/mmc/host/mmc_spi.c | 1 +
drivers/mmc/host/sdhci-sirf.c | 1 +
drivers/mmc/host/tmio_mmc_pio.c | 1 +
4 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/core/slot-gpio.c b/drivers/mmc/core/slot-gpio.c
index 5f89cb83d5f0..187f48a5795a 100644
--- a/drivers/mmc/core/slot-gpio.c
+++ b/drivers/mmc/core/slot-gpio.c
@@ -221,8 +221,6 @@ int mmc_gpio_request_cd(struct mmc_host *host, unsigned int gpio,
ctx->override_cd_active_level = true;
ctx->cd_gpio = gpio_to_desc(gpio);

- mmc_gpiod_request_cd_irq(host);
return 0;
diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index cc8d4a6099cd..e4a07546f8b6 100644
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1436,6 +1436,7 @@ static int mmc_spi_probe(struct spi_device *spi)
if (status != 0)
goto fail_add_host;
+ mmc_gpiod_request_cd_irq(mmc);

if (host->pdata && host->pdata->flags & MMC_SPI_USE_RO_GPIO) {
diff --git a/drivers/mmc/host/sdhci-sirf.c b/drivers/mmc/host/sdhci-sirf.c
index 17004531d089..b6db259aea9e 100644
--- a/drivers/mmc/host/sdhci-sirf.c
+++ b/drivers/mmc/host/sdhci-sirf.c
@@ -94,6 +94,7 @@ static int sdhci_sirf_probe(struct platform_device *pdev)
goto err_request_cd;
+ mmc_gpiod_request_cd_irq(host->mmc);

return 0;
diff --git a/drivers/mmc/host/tmio_mmc_pio.c b/drivers/mmc/host/tmio_mmc_pio.c
index faf0924e71cb..59d9a7249b2e 100644
--- a/drivers/mmc/host/tmio_mmc_pio.c
+++ b/drivers/mmc/host/tmio_mmc_pio.c
@@ -1103,6 +1103,7 @@ int tmio_mmc_host_probe(struct tmio_mmc_host **host,
return ret;
+ mmc_gpiod_request_cd_irq(mmc);

*host = _host;

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