Rafael J. Wysocki wrote: > On Wednesday 17 March 2010, Oren Laadan wrote: >> From: Matt Helsley <matthltc@xxxxxxxxxx> >> >> When the cgroup freezer is used to freeze tasks we do not want to thaw >> those tasks during resume. Currently we test the cgroup freezer >> state of the resuming tasks to see if the cgroup is FROZEN. If so >> then we don't thaw the task. However, the FREEZING state also indicates >> that the task should remain frozen. >> >> This also avoids a problem pointed out by Oren Ladaan: the freezer state >> transition from FREEZING to FROZEN is updated lazily when userspace reads >> or writes the freezer.state file in the cgroup filesystem. This means that >> resume will thaw tasks in cgroups which should be in the FROZEN state if >> there is no read/write of the freezer.state file to trigger this >> transition before suspend. >> >> NOTE: Another "simple" solution would be to always update the cgroup >> freezer state during resume. However it's a bad choice for several reasons: >> Updating the cgroup freezer state is somewhat expensive because it requires >> walking all the tasks in the cgroup and checking if they are each frozen. >> Worse, this could easily make resume run in N^2 time where N is the number >> of tasks in the cgroup. Finally, updating the freezer state from this code >> path requires trickier locking because of the way locks must be ordered. >> >> Instead of updating the freezer state we rely on the fact that lazy >> updates only manage the transition from FREEZING to FROZEN. We know that >> a cgroup with the FREEZING state may actually be FROZEN so test for that >> state too. This makes sense in the resume path even for partially-frozen >> cgroups -- those that really are FREEZING but not FROZEN. >> >> Reported-by: Oren Ladaan <orenl@xxxxxxxxxxxxxxx> >> Signed-off-by: Matt Helsley <matthltc@xxxxxxxxxx> >> Cc: Cedric Le Goater <legoater@xxxxxxx> >> Cc: Paul Menage <menage@xxxxxxxxxx> >> Cc: Li Zefan <lizf@xxxxxxxxxxxxxx> >> Cc: Rafael J. Wysocki <rjw@xxxxxxx> >> Cc: Pavel Machek <pavel@xxxxxx> >> Cc: linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > > Looks reasonable. > > Is anyone handling that already or do you want me to take it to my tree? Yes, please do. Thanks ! Oren. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
