linux-kernel - Re: [PATCH hw_breakpoint] percpu: add __percpu sparse annotations to hw

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Message-ID: <20100217163944.GC5041@nowhere>
Date:	Wed, 17 Feb 2010 17:39:49 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH hw_breakpoint] percpu: add __percpu sparse annotations
	to hw_breakpoint

On Wed, Feb 17, 2010 at 10:50:50AM +0900, Tejun Heo wrote:
> Add __percpu sparse annotations to hw_breakpoint.
> 
> These annotations are to make sparse consider percpu variables to be
> in a different address space and warn if accessed without going
> through percpu accessors.  This patch doesn't affect normal builds.
> 
> In kernel/hw_breakpoint.c, per_cpu(nr_task_bp_pinned, cpu)'s will
> trigger sprious noderef related warnings from sparse.  Changing it to
> &per_cpu(nr_task_bp_pinned[0], cpu) will work around the problem but
> deemed to ugly by the maintainer.  Leave it alone until better
> solution can be found.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> ---
> Frederic, can you please put this into the tree for hw_breakpoint?
> 
> Thanks.


Yeah, looks good, I'm queuing it.
Just few comments below, for nano-considerations.



>  	cpu_events = alloc_percpu(typeof(*cpu_events));
>  	if (!cpu_events)
> -		return ERR_PTR(-ENOMEM);
> +		return (void __percpu __force *)ERR_PTR(-ENOMEM);



Is this pattern common enough that we can think about a ERR_CPU_PTR ?




>  	sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler);
> -	if (IS_ERR(sample_hbp)) {
> -		ret = PTR_ERR(sample_hbp);
> +	if (IS_ERR((void __force *)sample_hbp)) {
> +		ret = PTR_ERR((void __force *)sample_hbp);


Same comments here, although I wouldn't like much a CPU_PTR_ERR or
IS_ERR_CPU.... CPP is just so poor in magic for that.

I must confess I miss a bit the old per_cpu prefix that guarded the implicit
separate namespace.

Anyway, I'm queuing it, thanks.

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