linux-kernel - Re: [PATCH V5 02/17] perf mmap: fix: recalculate size for overwrite mode.

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Date:   Thu, 1 Feb 2018 18:23:13 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     kan.liang@...el.com
Cc:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, wangnan0@...wei.com,
        jolsa@...nel.org, namhyung@...nel.org, ak@...ux.intel.com,
        yao.jin@...ux.intel.com
Subject: Re: [PATCH V5 02/17] perf mmap: fix: recalculate size for overwrite
 mode.

Em Thu, Jan 18, 2018 at 01:26:17PM -0800, kan.liang@...el.com escreveu:
> From: Kan Liang <kan.liang@...el.com>
> 
> In perf_mmap__push(), the 'size' need to be recalculated, otherwise the
> invalid data might be pushed to the record in overwrite mode.
> 
> The issue is introduced by commit 7fb4b407a124 ("perf mmap: Don't
> discard prev in backward mode").

In these cases, please add the Fixes tag, like:

Fixes: 7fb4b407a124 ("perf mmap: Don't discard prev in backward mode")

I'm doing it this time.

Thanks,

- Arnaldo
 
> When the ringbuffer is full in overwrite mode, backward_rb_find_range
> will be called to recalculate the 'start' and 'end'. The 'size' needs to
> be recalculated accordingly.
> 
> Unconditionally recalculate the 'size', not just for full ringbuffer in
> overwrite mode. Because,
> - There is no harmful to recalculate the 'size' for other cases.
> - The code of calculating 'start' and 'end' will be factored out later.
>   The new function does not need to return 'size'.
> 
> Signed-off-by: Kan Liang <kan.liang@...el.com>
> ---
>  tools/perf/util/mmap.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> index 05076e6..97cf4fa 100644
> --- a/tools/perf/util/mmap.c
> +++ b/tools/perf/util/mmap.c
> @@ -302,6 +302,8 @@ int perf_mmap__push(struct perf_mmap *md, bool overwrite,
>  			return -1;
>  	}
>  
> +	size = end - start;
> +
>  	if ((start & md->mask) + size != (end & md->mask)) {
>  		buf = &data[start & md->mask];
>  		size = md->mask + 1 - (start & md->mask);
> -- 
> 2.5.5