This is a note to let you know that I've just added the patch titled perf lock: Don't free "lock_seq_stat" if read_count isn't zero to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: perf-lock-don-t-free-lock_seq_stat-if-read_count-isn.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 5c968b82229b44710a313176763a3b2b5413adff Author: Leo Yan <leo.yan@xxxxxxxxxx> Date: Wed Nov 4 17:42:29 2020 +0800 perf lock: Don't free "lock_seq_stat" if read_count isn't zero [ 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> 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; }