Messages in this thread | | | Date | Thu, 23 Feb 2012 11:55:31 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [RFC][PATCH 0/7] PM: Implement autosleep and "wake locks", take2 |
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On 02/23/2012 03:40 AM, Rafael J. Wysocki wrote:
> On Wednesday, February 22, 2012, Srivatsa S. Bhat wrote: >> On 02/22/2012 10:19 AM, John Stultz wrote: >> >>> On Wed, 2012-02-22 at 00:31 +0100, Rafael J. Wysocki wrote: >>>> Hi all, >>>> >>>> After the feedback so far I've decided to follow up with a refreshed patchset. >>>> The first two patches from the previous one went to linux-pm/linux-next >>>> and I included the recent evdev patch from Arve (with some modifications) >>>> to this patchset for completness. >>> >>> Hey Rafael, >>> Thanks again for posting this! I've started playing around with it in a >>> kvm environment, and got the following warning after echoing off > >>> autosleep: >>> ... >>> PM: resume of devices complete after 185.615 msecs >>> PM: Finishing wakeup. >>> Restarting tasks ... done. >>> PM: Syncing filesystems ... done. >>> PM: Preparing system for mem sleep >>> Freezing user space processes ... >>> Freezing of tasks failed after 20.01 seconds (1 tasks refusing to freeze, wq_busy=0): >>> bash D ffff880015714010 >> >> >> Ah.. I think I know what is the problem here.. >> >> The kernel was freezing userspace processes and meanwhile, you wrote "off" >> to autosleep. So, as a result, this userspace process (bash) just now >> entered kernel mode. Unfortunately, the autosleep_lock is held for too long, >> that is, something like: >> >> acquire autosleep_lock >> modify autosleep_state >> <============== "A" >> pm_suspend or hibernate() >> >> release autosleep_lock >> >> At point marked "A", we should have released the autosleep lock and only then >> entered pm_suspend or hibernate(). Since the current code holds the lock and >> enters suspend/hibernate, the userspace process that wrote "off" to autosleep >> (or even userspace process that writes to /sys/power/state will end up waiting >> on autosleep_lock, thus failing the freezing operation.) >> >> So the solution is to always release the autosleep lock before entering >> suspend/hibernation. > > Well, the autosleep lock is intentionally held around suspend/hibernation in > try_to_suspend(), because otherwise it would be possible to trigger automatic > suspend right after user space has disabled it. >
Hmm.. I was just wondering if we could avoid holding yet another lock in the suspend/hibernate path, if possible..
> I think the solution is to make pm_autosleep_lock() do a _trylock() and > return error code if already locked. >
... and also do a trylock() in pm_autosleep_set_state() right?.... that is where John hit the problem..
By the way, I am just curious.. how difficult will this make it for userspace to disable autosleep? I mean, would a trylock mean that the user has to keep fighting until he finally gets a chance to disable autosleep?
Regards, Srivatsa S. Bhat
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