Patch "perf lock: Don't free "lock_seq_stat" if read_count isn't zero" has been added to the 5.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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 5.9-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-5.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 574db974aacbf776ecdadcfef3a86c23cd3f7fda
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 5cecc1ad78e1f..a2f1e53f37a7a 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -621,7 +621,7 @@ static int report_lock_release_event(struct 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;
 		}