Messages in this thread | | | Date | Fri, 16 Nov 2007 18:29:56 +0100 | From | "Franck Bui-Huu" <> | Subject | Re: apm emulation driver broken ? |
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On Nov 16, 2007 5:20 PM, Rafael J. Wysocki <rjw@sisk.pl> 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.
As I said, I'm not familiar with this code, so please correct me if I'm wrong.
BTW, how does try_to_freeze_tasks() deal with user land thread waiting in the UNINTERRUPTIBLE state ?
Thanks.
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