[PATCH 4.19 46/91] perf lock: Dont free "lock_seq_stat" if read_count isnt zero

Greg Kroah-Hartman
2020-11-23T12:31:56Z

From: Leo Yan <leo.yan@linaro.org>

[ 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@linaro.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20201104094229.17509-2-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 6e0189df2b3ba..0cb7f7b731fb0 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -620,7 +620,7 @@ 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