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

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Date:   Thu, 18 Jan 2018 13:26:17 -0800
From:   kan.liang@...el.com
To:     acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     wangnan0@...wei.com, jolsa@...nel.org, namhyung@...nel.org,
        ak@...ux.intel.com, yao.jin@...ux.intel.com,
        Kan Liang <kan.liang@...el.com>
Subject: [PATCH V5 02/17] perf mmap: fix: recalculate size for overwrite mode.

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").

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