read up:

http://en.wikipedia.org/wiki/Sparse

it was introduced to facilitate static source code checking, and the "attribute" itself is part of GCC:

http://www.unixwiz.net/techtips/gnu-c-attributes.html

Reading up here:

http://old.nabble.com/A-question-about-sparse%3A-how-to-use-__acquires()-and-__releases()-correctly---td20799721.html

http://www.gossamer-threads.com/lists/linux/kernel/680631

https://lkml.org/lkml/2006/8/22/325

my understanding is that the annotation will help u to identify whether is lock is to be release or acquired, and if u did not do it (eg, in a if-then loop, only one part release the lock, but not the other), locks contentions problem may happened - so the parser (sparse) will immediately highlight that.   normally not releasing a lock will lead to CPU hard-hanging, or CPU-reaching 100% utilization bugs.

and if the lock can be used for both purpose, then u have to double declare it (as release + acquire type):

http://old.nabble.com/linux-next%3A-manual-merge-of-the-percpu-tree-with-Linus'-tree-td26126413.html

On Mon, Oct 10, 2011 at 6:58 PM, venu <bvg_1@yahoo.com> wrote:
While going thro’ run time power management code in K39 power/runtime.c file, am seeing a function definition as given below. Any idea, what “__releases” & “__acquires” are doing in this function definition?
 
static int rpm_callback(int (*cb)(struct device *), struct device *dev)
                __releases(&dev->power.lock) __acquires(&dev->power.lock)
{
                int retval;
                ….
                return retval;
}

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--
Regards,
Peter Teoh