Re: [patch 1/3] Relay Reset Consumed

[Andy Whitcroft <apw@shadowen.org>]

On Wed, Mar 05, 2008 at 02:12:29PM -0800, Andrew Morton wrote:
> On Mon, 03 Mar 2008 15:51:50 -0800
> "David J. Wilder" <dwilder@us.ibm.com> wrote:
> 
> > This patch allows relay channels to be reset i.e. unconsumed.
> > Basically allows a 'rewind' function for flight-recorder tracing.
> > 
> > +void relay_reset_consumed(struct rchan *chan)
> > +{
> > +	unsigned int i;
> > +	struct rchan_buf *prev = NULL;
> > +
> > +	if (!chan)
> > +		return;
> > +
> > +	for (i = 0; i < NR_CPUS; i++) {
> 
> Use of NR_CPUS is usually wrong.  In this case it seems you should be using
> for_each_possible_cpu().
> 
> Also the existing usage of NR_CPUS in relay_subbufs_consumed() should be
> switched to using cpu_possible().
> 
> 
> New usage of NR_CPUS might be checkpatch-worthy, actually:
> 
> akpm:/usr/src/25> grep -l '^+.*NR_CPUS' patches/*.patch 
> patches/ext4-mm-mballoc-core.patch
> patches/git-kvm.patch
> patches/git-perfmon.patch
> patches/relay-reset-consumed.patch
> patches/x86-andi-git-x86.patch
> patches/x86-andi-smp-switch-optimize.patch
> 
> that's a sample of 1852 patches.
> 
> An appropriate warning would be "Usage of NR_CPUS is often wrong - should
> you be using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(),
> etc?".

That seems reasonable.  If we special case the definitions of NR_CPUS
and the use of them to define arrays of things both of which appear
reasonable,

	#define NR_CPUS 10
	int semid[NR_CPUS];

then it seems sensible to report this one:

	WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc
	#1: FILE: Z101.c:1:
	+       for (i = 0; i < NR_CPUS; i++)

This will be in the next push to -mm.

-apw