[PATCH 4.9 26/47] perf lock: Dont free "lock_seq_stat" if read_count isnt zero

[Greg Kroah-Hartman]

From: Leo Yan <leo.yan@xxxxxxxxxx>

[ Upstream commit b0e5a05cc9e37763c7f19366d94b1a6160c755bc ]

When execute command "perf lock report", it hits failure and outputs log
as follows:

  perf: builtin-lock.c:623: report_lock_release_event: Assertion `!(seq->read_count < 0)' failed.
  Aborted

This is an imbalance issue.  The locking sequence structure
"lock_seq_stat" contains the reader counter and it is used to check if
the locking sequence is balance or not between acquiring and releasing.

If the tool wrongly frees "lock_seq_stat" when "read_count" isn't zero,
the "read_count" will be reset to zero when allocate a new structure at
the next time; thus it causes the wrong counting for reader and finally
results in imbalance issue.

To fix this issue, if detects "read_count" is not zero (means still have
read user in the locking sequence), goto the "end" tag to skip freeing
structure "lock_seq_stat".

Fixes: e4cef1f65061 ("perf lock: Fix state machine to recognize lock sequence")
Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20201104094229.17509-2-leo.yan@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/perf/builtin-lock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index ce3bfb48b26f0..956b0aa916cfe 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -616,7 +616,7 @@ static int report_lock_release_event(struct perf_evsel *evsel,
 	case SEQ_STATE_READ_ACQUIRED:
 		seq->read_count--;
 		BUG_ON(seq->read_count < 0);
-		if (!seq->read_count) {
+		if (seq->read_count) {
 			ls->nr_release++;
 			goto end;
 		}
-- 
2.27.0