Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [RFC][PATCH 0/7] PM: Implement autosleep and "wake locks", take2 | Date | Thu, 23 Feb 2012 22:26:42 +0100 |
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On Thursday, February 23, 2012, Srivatsa S. Bhat wrote: > 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?
That's a good point, so I think it may be a good idea to do mutex_lock_interruptible() in pm_autosleep_set_state() instead.
Thanks, Rafael
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