On Sun, Jun 20, 2010 at 8:52 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
>
> What happens if the variable is completed while nobody is waiting for
> it? The next time somebody tries to wait, won't the wait terminate
> immediately?
>
Haven't tested it but will reply with the answer once I get a chance to test it.
>> I tried wait_for_completion instead, but now the kernel refuses to suspend.
>>
>> I have tried wait queues and mutexs with no success.
>>
>> Could anyone please point me how I can resolve this issue? Is there
>> any construct which can block inside the kernel during suspend/resume?
>
> Yes: The freezer.
>
>> Can there be a blocking call active while we suspend?
>
> Yes, in theory. In practice it's not a good idea, since the call
> wouldn't be able to distinguish between an actual signal and the onset
> of a suspend. You might end up with a call that ignores all signals
> and hence cannot be interrupted.
>
Just for the information of others on the list, here is what we did to
solve this issue, we designed a freezer-friendly wrapper around
wait_for_completion_interruptible()
<SNIP>
#define wait_for_completion_freezable(ptr_completion) \
({ \
int __retval; \
do { \
__retval = wait_for_completion_interruptible( \
ptr_completion); \
if (__retval && !freezing(current)) \
break; \
} while (try_to_freeze()); \
__retval; \
})
</SNIP>
Thanks
Suresh
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