linux-kernel - [tip:perf/urgent] perf mmap: Recalculate size for overwrite mode

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Date:   Fri, 16 Feb 2018 01:34:54 -0800
From:   tip-bot for Kan Liang <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, peterz@...radead.org, acme@...hat.com,
        wangnan0@...wei.com, kan.liang@...el.com, hpa@...or.com,
        namhyung@...nel.org, yao.jin@...ux.intel.com, jolsa@...nel.org,
        linux-kernel@...r.kernel.org, mingo@...nel.org, ak@...ux.intel.com
Subject: [tip:perf/urgent] perf mmap: Recalculate size for overwrite mode

Commit-ID:  dc6c35c679e96987dc83a003f30bc2cc33c84c00
Gitweb:     https://git.kernel.org/tip/dc6c35c679e96987dc83a003f30bc2cc33c84c00
Author:     Kan Liang <kan.liang@...el.com>
AuthorDate: Thu, 18 Jan 2018 13:26:17 -0800
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Thu, 15 Feb 2018 09:51:57 -0300

perf mmap: Recalculate size for overwrite mode

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").

When the ring buffer 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 ring buffer 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>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Jin Yao <yao.jin@...ux.intel.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Wang Nan <wangnan0@...wei.com>
Fixes: 7fb4b407a124 ("perf mmap: Don't discard prev in backward mode")
Link: http://lkml.kernel.org/r/1516310792-208685-3-git-send-email-kan.liang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.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);