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From: Suresh Rajashekara <suresh.raj+linuxomap@gmail.com>
Date: Sat, 26 Jun 2010 21:08:07 -0700
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Subject: Re: [linux-pm] wait_for_completion_interruptible does not wait !!
To: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-omap@vger.kernel.org, linux-pm@lists.linux-foundation.org,
       LKML <linux-kernel@vger.kernel.org>,
       vivin uthappa <vivinuthappa@gmail.com>,
       Sudhakar R <sudhakar.raj@gmail.com>
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On Sun, Jun 20, 2010 at 8:52 AM, Alan Stern <stern@rowland.harvard.edu> 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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