linux-kernel - Re: [RFC PATCH v2 08/12] arm64: cmpxchg: Include build_bug.h instead of bug.h for BUILD

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Message-ID: <20180227173322.GK29123@arm.com>
Date:   Tue, 27 Feb 2018 17:33:23 +0000
From:   Will Deacon <will.deacon@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        yamada.masahiro@...ionext.com, mingo@...nel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v2 08/12] arm64: cmpxchg: Include build_bug.h instead
 of bug.h for BUILD_BUG

On Mon, Feb 26, 2018 at 03:48:49PM +0000, Mark Rutland wrote:
> On Mon, Feb 26, 2018 at 03:04:56PM +0000, Will Deacon wrote:
> > Having asm/cmpxchg.h pull in linux/bug.h is problematic because this
> > ends up pulling in the atomic bitops which themselves may be built on
> > top of atomic.h and cmpxchg.h.
> > 
> > Instead, just include build_bug.h for the definition of BUILD_BUG.
> 
> We also use VM_BUG_ON(), defined in <linux/mmdebug.h>, which includes
> <linux/bug.h>.
> 
> ... so I think we still have some fragility here, albeit no worse than before.
> 
> We also miss includes for:
> 
> * <linux/percpu-defs.h> (raw_cpu_ptr)
> * <linux/preempt.h> (preempt_disable, preempt_enable)

Hmm, we can't include this one because it pulls in linux/bitops.h. I've
moved the percpu cmpxchg stuff into asm/percpu.h, but that too is missing
the linux/preempt.h #include, so I've added that as well.

Generally, I think if we want to clean up our #includes then that's better
done as a separate series rather than as a piecemeal effort, which will
likely fail to identify many of the underlying problems.

Will