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    SubjectRe: Bug in disk event polling
    (cc'ing Rafael)

    Hello, Alan.

    On Fri, Feb 10, 2012 at 03:31:20PM -0500, Alan Stern wrote:
    > Don't ask me why this hasn't shown up earlier... There's a big fat bug
    > in the implementation of disk event polling.
    > The polling is done using the system_nrt_wq work queue, which isn't
    > freezable. As a result, polling continues while the system is
    > preparing for suspend or hibernation.
    > Obviously I/O to suspended devices doesn't work well. Somewhat less
    > obviously, error recovery for the failed I/O attempts can interfere
    > with normal system resume.

    Hmmm.... I see. Yeah, that can be a problem.

    > You can see this for yourself easily enough by suspending or
    > hibernating while a USB flash drive is plugged in. You don't even need
    > to go through the full suspend procedure; the first two stages are
    > enough (echo devices >/sys/power/pm_test). Check the system log
    > afterward; most likely you'll find the flash drive got errors and had
    > to be unregistered and re-enumerated.

    Do you happen to have log of such failure? Polilng failure itself
    shouldn't lead to such failure mode.

    > I have verified that changing all occurrences of system_nrt_wq in
    > block/genhd.c to system_freezable_wq fixes the bug. However this may
    > not be the way you want to solve it; you may prefer to have a freezable
    > non-reentrant work queue.

    Please feel free to send out a patch to fix the issue. :)



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