From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH] mmc: don't request CD IRQ until mmc_start_host() Date: Thu, 18 Sep 2014 10:49:00 -0600 Message-ID: <541B0CFC.1000005@wwwdotorg.org> References: <1410542338-24565-1-git-send-email-swarren@wwwdotorg.org> <5419E7B6.7020708@wwwdotorg.org> <541A6CAD.1020001@intel.com> <541A8062.3020008@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from avon.wwwdotorg.org ([70.85.31.133]:45122 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756218AbaIRQsl (ORCPT ); Thu, 18 Sep 2014 12:48:41 -0400 In-Reply-To: <541A8062.3020008@intel.com> Sender: linux-mmc-owner@vger.kernel.org List-Id: linux-mmc@vger.kernel.org To: Adrian Hunter , Ulf Hansson Cc: Chris Ball , linux-mmc , "linux-kernel@vger.kernel.org" , Stephen Warren , Russell King , Alexandre Courbot , Linus Walleij 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 wrote: >>>>> From: Stephen Warren >>>>> >>>>> 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.