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    SubjectRe: [linux-pm] Is it supposed to be ok to call del_gendisk while userspace is frozen?
    Date
    On Sunday 16 May 2010, Nigel Cunningham wrote:
    > Hi.
    >
    > On 16/05/10 06:30, Rafael J. Wysocki wrote:
    > > On Saturday 15 May 2010, Alan Stern wrote:
    > >> On Thu, 13 May 2010, Matt Reimer wrote:
    > >>
    > >>>> I don't see anything wrong with the patch itself, but I dislike the
    > >>>> description. Devices can come and go from any hotpluggable bus, not
    > >>>> just MMC/SD. That just happens to be the first place the problem was
    > >>>> observed.
    > >>>
    > >>> Good point. How about this?
    > >>>
    > >>> Matt
    > >>>
    > >>> From 813bd223e5a2fa577b9e64ddf12654a93d0aab8b Mon Sep 17 00:00:00 2001
    > >>> From: Matt Reimer<mreimer@sdgsystems.com>
    > >>> Date: Thu, 13 May 2010 14:36:54 -0700
    > >>> Subject: [PATCH] fs: prevent hang on suspend/resume when MMC/SD card present
    > >>>
    > >>> Devices can come and go bus during suspend or resume, when the
    > >>> writeback thread is frozen, resulting in a hang. Prevent the hang
    > >>> by thawing the writeback thread in del_gendisk().
    > >>
    > >> I would have said "the block layer's writeback thread", but this is
    > >> okay.
    > >
    > > OK, so now I have a question who's going to take the patch.
    >
    > I object to the patch.
    >
    > Tell the patch it ought to exit once thawed, by all means.

    I'm not sure what you mean. Care to explain?

    > Make the patch unfreezeable to begin with, by all means.

    That wouldn't work.

    > But don't go down the path of having $random_code_path unfreeze a
    > thread. That will lead to unpredictability, confusion and bugs.

    As a general rule, I agree, but this particular case is somewhat special.

    > If you know a disk is going to be unregistered during resume,

    How do we check that, exactly?

    > use the hooks early in the suspend / hibernate process to block new I/O and
    > flush what's already there so that there's no need to block on the
    > writeback thread, and/or no need to have the writeback thread frozen.

    I'm not sure if that's realistic. Do you have a specific implementation in
    mind?

    Rafael


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