linux-kernel - Re: Is there a primitive to atomically release a spinlock and go to sleep?

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Message-ID: <4C7F08ED.9010901@mit.edu>
Date:	Wed, 01 Sep 2010 22:16:13 -0400
From:	Andy Lutomirski <luto@....edu>
To:	David Nicol <davidnicol@...il.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Is there a primitive to atomically release a spinlock and go
 to sleep?

David Nicol wrote:
> I'm trying to do something involving multiple kthreads in an ioctl
> handler, and I want to avoid the
> race condition between the third and fourth steps of
> 
>     acquire mutex
>     add &self to a list of threads which will get awakened by
> something else that is also aware of this list
>     release mutex
>     go to sleep
> 
> Is there a standard atomic go-to-sleep function that takes as a
> parameter a pointer to  spinlock to release after its state is set to
> TASK_INTERRUPTIBLE?

That wouldn't be enough -- the other thread could try to wake you up before you're even in the list of threads.

Look at wait_event_*() or read this:

http://book.chinaunix.net/special/ebook/PrenticeHall/PrenticeHallPTRTheLinuxKernelPrimer/0131181637/ch03lev1sec7.html

--Andy
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