• Stephen Warren's avatar
    mmc: don't request CD IRQ until mmc_start_host() · d4d11449
    Stephen Warren authored
    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 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@arm.linux.org.uk>
    Cc: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Alexandre Courbot <acourbot@nvidia.com>
    Cc: Linus Walleij <linus.walleij@linaro.org>
    Signed-off-by: default avatarStephen Warren <swarren@nvidia.com>
    Acked-by: default avatarAdrian Hunter <adrian.hunter@intel.com>
    Cc: <stable@vger.kernel.org> # v3.15+
    Signed-off-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
    d4d11449
slot-gpio.c 9.99 KB