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Date: Fri, 10 Feb 2012 15:31:20 -0500 (EST) From: Alan Stern <stern@...land.harvard.edu> To: Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk> cc: Linux-pm mailing list <linux-pm@...r.kernel.org>, Kernel development list <linux-kernel@...r.kernel.org> Subject: Bug in disk event polling Tejun: 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. 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. 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. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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