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    SubjectRe: [PATCH] MMC: fix hang if card was removed during suspend and unsafe resume was enabled
    On Fri, 05 Feb 2010 10:31:42 +0200 Maxim Levitsky <maximlevitsky@gmail.com> wrote:

    > On Thu, 2010-02-04 at 16:09 -0800, Andrew Morton wrote:
    > > On Fri, 5 Feb 2010 01:18:15 +0200 Maxim Levitsky <maximlevitsky@gmail.com> wrote:
    > >
    > > > Currently removal of the card leads to del_disk called indirectly by mmc core.
    > > > This function expects userspace to be running, which isn't when .resume is called
    > > >
    > > > Fix that by removing the code that did that in mmc_resume_host. It is possible
    > > > because card detection logic will kick it later and remove the card.
    > >
    > > I don't really understand. The above implies that to trigger this bug,
    > > one needs to physically remove the card during a resume operation. ie:
    > > a human-vs-computer race. Sounds unlikely?
    > >
    > > So... exactly what steps does the user need to take to trigger this
    >
    > Sorry for describing this poorly.
    > The steps are:
    >
    > -> Have a kernel with CONFIG_MMC_UNSAFE_RESUME
    > -> Insert MMC/SD card
    > -> Suspend/hibernate the system
    > -> While system is hibernated/suspended pull the card off
    > -> Resume the system
    > -> Hang
    >
    >
    > if CONFIG_MMC_UNSAFE_RESUME is set, mmc core allows the user to
    > suspend/resume the card normally assuming he won't change the card or
    > modify it in another system. The former case is actually handled quite
    > well.
    >
    > if CONFIG_MMC_UNSAFE_RESUME isn't set, it removes the card during
    > suspend, and I now think (and will test) that this will still hang the
    > system this time on suspend.
    >
    > Maybe we can make del_disk behave well if called with userspace frozen?
    > After all if user calls it, very likely that hardware is absent thus
    > there is no point in syncing (which I think triggers the hang)....
    >

    There is no del_disk in the kernel. Let's be more specific (and
    accurate!) about the hang. I assume it's
    mmc_remove_card->device_del->kobject_uevent?

    Yes, I'd have thought that it would be a good idea for the
    kobject_uevent code (or lower, in call_usermodehelper) to take avoiding
    action if userspace is frozen. However such action would probably
    involve doing a WARN_ON() too, so we'd still need MMC changes to avoid
    that.




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