linux-kernel - Re: Synchronization mechanism between wait_for_completion_interruptible

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Message-ID: <20150306084807.GC22716@dhcp22.suse.cz>
Date:	Fri, 6 Mar 2015 09:48:07 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Naveen Kumar Parna <pnaveenkos@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Synchronization mechanism between
 wait_for_completion_interruptible_timeout() & complete()

On Fri 06-03-15 14:04:53, Naveen Kumar Parna wrote:
> Thanks Michal.
> 
> Now I am clearing x->done to zero before
> wait_for_completion_interruptible_timeout.

You shouldn't touch this internal thing. Why would you want that
anyway? If x->done > 0 then there has been something completed.

> On Thu, Mar 5, 2015 at 6:53 PM, Michal Hocko <mhocko@...e.cz> wrote:
> > On Wed 04-03-15 18:46:43, Naveen Kumar Parna wrote:
> >> Hello,
> >>
> >> I have a question regarding the synchronization mechanism between
> >> wait_for_completion_interruptible_timeout() & complete(). I used
> >> complete() API in the ISR Tx interrupt path and
> >> wait_for_completion_interruptible_timeout() in struct file_operations
> >> .write method.
> >>
> >> Let assume a scenario in which Tx interrupt occurred and ISR called
> >> complete() API before any process actually blocked at write method on
> >> wait_for_completion_interruptible_timeout().
> >>
> >> After a few milli seconds, a process called write() API. Does it gets
> >> blocked on wait_for_completion_interruptible_timeout() for completion
> >> of a specific task to be signaled from new Tx interrupt?
> >
> > No, see do_wait_for_common resp. complete and x->done handling.
> >
> > --
> > Michal Hocko
> > SUSE Labs

-- 
Michal Hocko
SUSE Labs
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