linux-kernel - RE: [PATCH] mmc: core: Fix hanging on I/O during system suspend for removable cards

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Date:   Mon, 22 Mar 2021 16:21:13 +0900
From:   "Kiwoong Kim" <kwmad.kim@...sung.com>
To:     "'Ulf Hansson'" <ulf.hansson@...aro.org>,
        <linux-mmc@...r.kernel.org>,
        "'Rafael J . Wysocki'" <rjw@...ysocki.net>
Cc:     "'Adrian Hunter'" <adrian.hunter@...el.com>,
        "'Linus Walleij'" <linus.walleij@...aro.org>,
        "'Wolfram Sang'" <wsa+renesas@...g-engineering.com>,
        <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        "'Android Kernel Team'" <kernel-team@...roid.com>,
        <stable@...r.kernel.org>,
        이상현 <sh425.lee@...sung.com>,
        서승철 <sc.suh@...sung.com>,
        서호영 <hy50.seo@...sung.com>,
        김병훈 <bhoon95.kim@...sung.com>
Subject: RE: [PATCH] mmc: core: Fix hanging on I/O during system suspend for
 removable cards

> The mmc core uses a PM notifier to temporarily during system suspend, turn
> off the card detection mechanism for removal/insertion of (e)MMC/SD/SDIO
> cards. Additionally, the notifier may be used to remove an SDIO card
> entirely, if a corresponding SDIO functional driver don't have the system
> suspend/resume callbacks assigned. This behaviour has been around for a
> very long time.
> 
> However, a recent bug report tells us there are problems with this
> approach. More precisely, when receiving the PM_SUSPEND_PREPARE
> notification, we may end up hanging on I/O to be completed, thus also
> preventing the system from getting suspended.
> 
> In the end what happens, is that the cancel_delayed_work_sync() in
> mmc_pm_notify() ends up waiting for mmc_rescan() to complete - and since
> mmc_rescan() wants to claim the host, it needs to wait for the I/O to be
> completed first.
> 
> Typically, this problem is triggered in Android, if there is ongoing I/O
> while the user decides to suspend, resume and then suspend the system
> again. This due to that after the resume, an mmc_rescan() work gets punted
> to the workqueue, which job is to verify that the card remains inserted
> after the system has resumed.
> 
> To fix this problem, userspace needs to become frozen to suspend the I/O,
> prior to turning off the card detection mechanism. Therefore, let's drop
> the PM notifiers for mmc subsystem altogether and rely on the card
> detection to be turned off/on as a part of the system_freezable_wq, that
> we are already using.
> 
> Moreover, to allow and SDIO card to be removed during system suspend,
> let's manage this from a ->prepare() callback, assigned at the
> mmc_host_class level. In this way, we can use the parent device (the
> mmc_host_class device), to remove the card device that is the child, in
> the
> device_prepare() phase.
> 
> Reported-by: Kiwoong Kim <kwmad.kim@...sung.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>


Reviewed-by: Kiwoong Kim <kwmad.kim@...sung.com>

Thanks.
Kiwoong Kim