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Date: Tue, 24 Mar 2015 12:07:54 +0100
From: Jiri Olsa <jolsa@redhat.com>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        linux-kernel@vger.kernel.org, David Ahern <dsahern@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Namhyung Kim <namhyung@gmail.com>, Paul Mackerras <paulus@samba.org>,
        Stephane Eranian <eranian@google.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH V6 02/25] perf evlist: Add initial support for mmapping
 an AUX area buffer
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On Mon, Mar 16, 2015 at 02:41:24PM +0200, Adrian Hunter wrote:

SNIP

> +#include <linux/bitops.h>
> +#include <linux/log2.h>
> +
> +#include "../perf.h"
> +#include "util.h"
> +#include "evlist.h"
> +#include "cpumap.h"
> +#include "thread_map.h"
> +#include "auxtrace.h"
> +
> +int auxtrace_mmap__mmap(struct auxtrace_mmap *mm,
> +			struct auxtrace_mmap_params *mp,
> +			void *userpg, int fd)
> +{
> +#if BITS_PER_LONG != 64 && !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT)
> +	pr_err("Cannot use AUX area tracing mmaps\n");
> +	return -1;
> +#endif
> +
> +	mm->userpg = userpg;
> +	mm->mask = mp->mask;
> +	mm->len = mp->len;
> +	mm->prev = 0;
> +	mm->idx = mp->idx;
> +	mm->tid = mp->tid;
> +	mm->cpu = mp->cpu;
> +
> +	if (!mp->len) {
> +		mm->base = NULL;

is it just for safety, or could mm->base be != NULL in here?
maybe good place to use WARN_ON check?

jirka