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 22:32:58 +0100 |
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On Thursday, February 23, 2012, Rafael J. Wysocki wrote: > 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.
Now that I think of it, perhaps it's a good idea to just make pm_autosleep_lock() do mutex_lock_interruptible() _and_ make pm_autosleep_set_state() use pm_autosleep_lock().
What do you think?
Rafael
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