On Friday, 16 of November 2007, Franck Bui-Huu wrote: > On Nov 16, 2007 5:20 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > > > > The freezer doesn't regard the current task as freezable. > > > > > Hmm, I don't get your point. > > If I understood this driver correctly, several processes can be > waiting for a suspend event by reading /dev/apm_bios, apmd (the _user_ > space daemon) can be one of them. > > Then another process asks to suspend the system by calling 'apm -s', > which results in a apm_ioctl() call. This process will basically > execute: > > err = queue_suspend_event(APM_USER_SUSPEND, as); > flags = current->flags; > wait_event_interruptible(apm_suspend_waitqueue, > as->suspend_state == SUSPEND_DONE); > > It's basically waiting for the waiters to ack the event. But it won't > be the process that is going to suspend the system, right ? > > So now all waiting processes are waken up and need to acknolwedge the > event for the system to actually suspend. So they need to call > apm_ioctl(). They'll basically do: > > flags = current->flags; > wait_event(apm_suspend_waitqueue, > as->suspend_state == SUSPEND_DONE); > > Except for the last acknowledging process which will do instead: > > apm_suspend(); > > It's a call to pm_suspend(). > > So you can see that the process which initiates the suspend, the one > that calls 'apm -s', is not the current process but is going to be > waken up by the fake signal sent by freeze_task(). > > One of the consequence I can see is at this time 'as->result' won't be > setup, so the return value of apm_ioctl() may be wrong. Ah, that. Yes, I see your point. However, using PF_NOFREEZE to prevent this from happening doesn't seem to be a good idea. I'd probably use wait_event_freezable() (defined in include/linux/freezer.h) for that. > As I said, I'm not familiar with this code, so please correct me if > I'm wrong. No, you're not wrong and I have overlooked the problem. > BTW, how does try_to_freeze_tasks() deal with user land thread waiting > in the UNINTERRUPTIBLE state ? It tries to send them fake signals and waits for them to freeze. If they don't freeze within the timeout, it fails and clears their TIF_FREEZE bits. Greetings, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
