linux-kernel - [PATCH] perf mmap: Fix accessing unmapped mmap in perf_mmap__read

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Date:   Mon, 26 Mar 2018 09:42:09 -0400
From:   kan.liang@...ux.intel.com
To:     acme@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org
Cc:     jolsa@...nel.org, namhyung@...nel.org, wangnan0@...wei.com,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH] perf mmap: Fix accessing unmapped mmap in perf_mmap__read_done()

From: Kan Liang <kan.liang@...ux.intel.com>

There is segmentation fault when running perf trace. For example,
  [root@...et e]# perf trace -e *chdir -o /tmp/bla perf report
  --ignore-vmlinux -i ../perf.data

The perf_mmap__consume() could unmap the mmap. It needs to check the
refcnt in perf_mmap__read_done().

Fixes: ee023de05f35 ("perf mmap: Introduce perf_mmap__read_done()")
Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
---
 tools/perf/util/mmap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index 38ca3ff..f6cfc52 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -317,5 +317,11 @@ int perf_mmap__push(struct perf_mmap *md, void *to,
  */
 void perf_mmap__read_done(struct perf_mmap *map)
 {
+	/*
+	 * Check if event was unmapped due to a POLLHUP/POLLERR.
+	 */
+	if (!refcount_read(&map->refcnt))
+		return;
+
 	map->prev = perf_mmap__read_head(map);
 }
-- 
2.4.11