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

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Date:	Sat, 13 Oct 2012 11:41:52 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 01:36:28PM -0700, Josh Triplett wrote:
> 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.

The kernel specific macros should be documented in:

    Documentation/sparse.txt

For now only __bitwise is documentd, but when we introduce new
sparse annotation macros in the kernel the documentation should
be mandatory.

	Sam
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