Date: Tue, 9 Oct 2012 13:36:28 -0700
From: Josh Triplett <josh@joshtriplett.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-sparse@vger.kernel.org,
        Ed Cashin <ecashin@coraid.com>, Christopher Li <sparse@chrisli.org>,
        Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH] linux/compiler.h: Add __must_hold macro for functions
 called with a lock held
Message-ID: <20121009203628.GB3616@jtriplet-mobl1>
References: <20121008020610.GA9197@leaf>
 <20121009130637.5e61078f.akpm@linux-foundation.org>
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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@joshtriplett.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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