utrace_resume(UTRACE_REPORT) always calls utrace_reset() because
start_callback() obviously can't clear report->spurious when
event == 0.
Change start_callback() to correctly clear ->spurious in this case.
We could probably clear it in utrace_resume() unconditionally after
reporting loop, but this is not exactly right if there are no engines
which have QUIESCE in engine->flags.
utrace_get_signal() probably has the same problem.
Note: utrace_control(DETACH) does utrace_do_stop() and sets UTRACE_REPORT
if the tracee is not stopped. It also does mark_engine_detached() which
does not set QUIESCE in target->utrace_flags. This means we rely on
report.spurious which should provoke utrace_reset() from utrace_resume()
if target->utrace_flags doesn't have QUIESCE. A bit too subtle, imho.
Also, UTRACE_REPORT can be lost because of UTRACE_INTERRUPT or normal
signal: utrace_get_signal() checks "utrace_flags & UTRACE_EVENT(QUIESCE)"
and returns otherwise. This should be fixed somehow. This check is wrong
anyway, but it is not clear how we can fix the race with DETACH.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/utrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- kstub/kernel/utrace.c~10_utrace_resume_and_spurious 2010-08-18
19:00:50.000000000 +0200
+++ kstub/kernel/utrace.c 2010-08-18 19:41:05.000000000 +0200
@@ -1540,7 +1540,7 @@ static const struct utrace_engine_ops *s
if (want & ENGINE_STOP)
report->action = UTRACE_STOP;
- if (want & event) {
+ if (want & (event ?: UTRACE_EVENT(QUIESCE))) {
report->spurious = false;
return ops;
}
