linux-kernel - Re: [PATCH 4/4] perf tools: Retry mapping buffers readonly on EACCES

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Date:	Fri, 14 Jun 2013 11:08:40 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Robert Richter <rric@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>, Jiri Olsa <jolsa@...hat.com>,
	linux-kernel@...r.kernel.org,
	Robert Richter <robert.richter@...xeda.com>
Subject: Re: [PATCH 4/4] perf tools: Retry mapping buffers readonly on EACCES

Hi Robert,

On Fri, 31 May 2013 11:16:25 +0200, Robert Richter wrote:
> From: Robert Richter <robert.richter@...xeda.com>
>
> Persistent event buffers may only be mmapped readonly. Thus, retry
> mapping it readonly if mmap returns EACCES after trying to mmap
> writable.
>
> Signed-off-by: Robert Richter <robert.richter@...xeda.com>
> ---
>  tools/perf/builtin-record.c | 7 ++++++-
>  tools/perf/builtin-top.c    | 8 ++++++--
>  tools/perf/perf.h           | 1 +
>  3 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index cdf58ec..916776d 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -255,7 +255,12 @@ try_again:
>  		goto out;
>  	}
>  
> -	if (perf_evlist__mmap(evlist, opts->mmap_pages, false) < 0) {
> +try_again2:
> +	if (perf_evlist__mmap(evlist, opts->mmap_pages, opts->mmap_ro) < 0) {
> +		if (!opts->mmap_ro && errno == EACCES) {
> +			opts->mmap_ro = true;
> +			goto try_again2;
> +		}
>  		if (errno == EPERM) {
>  			pr_err("Permission error mapping pages.\n"
>  			       "Consider increasing "
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index 67bdb9f..2a5757d 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -899,8 +899,12 @@ try_again:
>  			goto out_err;
>  		}
>  	}
> -
> -	if (perf_evlist__mmap(evlist, opts->mmap_pages, false) < 0) {
> +try_again2:
> +	if (perf_evlist__mmap(evlist, opts->mmap_pages, opts->mmap_ro) < 0) {
> +		if (!opts->mmap_ro && errno == EACCES) {
> +			opts->mmap_ro = true;
> +			goto try_again2;
> +		}
>  		ui__error("Failed to mmap with %d (%s)\n",
>  			    errno, strerror(errno));
>  		goto out_err;


You will need this also:


@@ -161,7 +161,8 @@ static int perf_record__mmap_read(struct perf_record *rec,
        }
 
        md->prev = old;
-       perf_mmap__write_tail(md, old);
+       if (!rec->opts.mmap_ro)
+               perf_mmap__write_tail(md, old);
 
 out:
        return rc;


-- 
Thanks,
Namhyung
--
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