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    Subject[PATCH 4.14 28/60] perf lock: Dont free "lock_seq_stat" if read_count isnt zero
    Date
    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 fe69cd6b89e1a..6140b0548ad7d 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


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