Messages in this thread | | | Date | Fri, 10 Feb 2012 12:46:52 -0800 | From | Tejun Heo <> | Subject | Re: Bug in disk event polling |
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(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. :)
Thanks.
-- tejun
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