Hi Jiri， Thanks for your reply. On 2019/5/7 16:51, Jiri Olsa wrote: > On Fri, May 03, 2019 at 10:35:55AM +0800, Wei Li wrote: >> After thread is added to machine->threads[i].dead in >> __machine__remove_thread, the machine->threads[i].dead is freed >> when calling free(session) in perf_session__delete(). So it get a >> Segmentation fault when accessing it in thread__put(). >> >> In this patch, we delay the perf_session__delete until all threads >> have been deleted. >> >> This can be reproduced by following steps: >> ulimit -c unlimited >> export MALLOC_MMAP_THRESHOLD_=0 > > what's this for?
When we set env "MALLOC_MMAP_THRESHOLD_=0"，the memory-allocation functions employ mmap instead of increasing the program break using sbrk what may be maintained with cache. Thus it can report "Segmentation fault" immediately when going into this use-after-free code. > >> perf sched record sleep 10 >> perf sched latency --sort max >> Segmentation fault (core dumped) >> >> Signed-off-by: Zhipeng Xie <[email protected]> >> Signed-off-by: Wei Li <[email protected]> >> --- >> tools/perf/builtin-sched.c | 44 ++++++++++++++++++++++++++++++++++++-- >> 1 file changed, 42 insertions(+), 2 deletions(-) >> >> diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c >> index cbf39dab19c1..17849ae2eb1e 100644 >> --- a/tools/perf/builtin-sched.c >> +++ b/tools/perf/builtin-sched.c >> @@ -3130,11 +3130,48 @@ static void perf_sched__merge_lat(struct perf_sched >> *sched) >> static int perf_sched__lat(struct perf_sched *sched) >> { >> struct rb_node *next; >> + const struct perf_evsel_str_handler handlers[] = { >> + { "sched:sched_switch", process_sched_switch_event, }, >> + { "sched:sched_stat_runtime", process_sched_runtime_event, }, >> + { "sched:sched_wakeup", process_sched_wakeup_event, }, >> + { "sched:sched_wakeup_new", process_sched_wakeup_event, }, >> + { "sched:sched_migrate_task", process_sched_migrate_task_event, >> }, >> + }; >> + struct perf_session *session; >> + struct perf_data data = { >> + .file = { >> + .path = input_name, >> + }, > > I can't compile this: > > builtin-sched.c: In function ‘perf_sched__lat’: > builtin-sched.c:3144:12: error: initialization discards ‘const’ qualifier > from pointer target type [-Werror=discarded-qualifiers] > .path = input_name, > Sorry, this place has been changed recently in mainline code, i will update to the latest code. > >> + .mode = PERF_DATA_MODE_READ, >> + .force = sched->force, >> + }; >> + int rc = -1; >> >> setup_pager(); >> >> - if (perf_sched__read_events(sched)) > > so it's basically perf_sched__read_events code in here now, right? > > might be better to add __perf_sched__read_events function > that would take session argument, something like: > > session = perf_session__new(&data, false, &sched->tool); > ... > __perf_sched__read_events(sched, session) > ... > perf_session__delete(session); > > to avoid the code ducplication Yes, what you suggest is reasonable, i will send a v2 with your suggestion soon. Thanks， Wei
