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.
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.
Franck
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