Messages in this thread | | | Date | Tue, 3 Nov 2020 10:29:44 +0800 | From | Leo Yan <> | Subject | Re: [PATCH v2 2/2] perf lock: Don't free "lock_seq_stat" if read_count isn't zero |
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On Mon, Nov 02, 2020 at 05:56:26PM +0100, Jiri Olsa wrote: > On Wed, Oct 21, 2020 at 08:39:48AM +0800, Leo Yan wrote: > > 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> > > --- > > 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 5cecc1ad78e1..a2f1e53f37a7 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++; > > it seems ok, but I fail to see what's nr_release for > the point is just to skip the removal of seq right?
To be honest, I'm not sure if I understand your question :)
Either remove "seq" or not, "nr_release" will be increased. When remove "seq", the code line [1] will increase '1' for "nr_release"; when skip to remove "seq", "nr_release" is also increased 1 [2]. So I don't see the logic issue for "nr_release", do I miss anything?
Another side topic is the four metrics "nr_acquire", "nr_release", "nr_readlock", "nr_trylock" have been accounted, but they are not really used for output final result. I'd like to defer this later as a task for refine the output metrics.
Thanks, Leo
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/builtin-lock.c#n641 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/builtin-lock.c#n625
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