linux-kernel - Re: [PATCH] linux/compiler.h: Add __must_hold macro for functions called with a lock held

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Date:	Tue, 9 Oct 2012 13:36:28 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org,
	Ed Cashin <ecashin@...aid.com>,
	Christopher Li <sparse@...isli.org>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] linux/compiler.h: Add __must_hold macro for functions
 called with a lock held

On Tue, Oct 09, 2012 at 01:06:37PM -0700, Andrew Morton wrote:
> On Sun, 7 Oct 2012 19:06:10 -0700
> Josh Triplett <josh@...htriplett.org> wrote:
> 
> > linux/compiler.h has macros to denote functions that acquire or release
> > locks, but not to denote functions called with a lock held that return
> > with the lock still held.  Add a __must_hold macro to cover that case.
> 
> hum.  How does this work?  Any code examples and sample sparse output? 
> Does it apply to all lock types, etc?

It applies to all the same lock types that __acquires and __releases
apply to: currently everything since Sparse doesn't actually do anything
with the parameter, just the context value.

Various code examples already exist in the kernel tree for __acquires
and __releases, and the mailing list contains many reports of the Sparse
context warnings.

Just as __acquires and __release annotate functions that return with a
lock acquired and get called with a lock that they drop (respectively),
__must_hold annotates a function called with a lock acquired that return
with that lock still acquired.

> IOW, where is all this stuff documented?

The Sparse manpage documents the context bits reasonably well.  Other
than that, nowhere that I know of other than the Sparse testsuite and
the source trees of projects like Linux that use Sparse.

- Josh Triplett
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