Suppose that engine->flags == UTRACE_EVENT(EXEC), QUIESCE bit is not set.
1. start_callback() reads want = engine->flags (== EXEC)
2. mark_engine_detached() sets engine->ops = &utrace_detached_ops
3. start_callback() gets ops = utrace_detached_ops
After that start_callback() skips "if (want & UTRACE_EVENT(QUIESCE))"
block and returns utrace_detached_ops, then ->report_exec == NULL
will be called.
This is the minimal temporary ugly fix for now, we should certainly
cleanup and simplify this logic. The barriers in mark_engine_detached()
and in start_callback() can't help and should be removed. If we ignore
utrace_get_signal() we do not even need utrace_detached_quiesce(),
start_callback() could just do
ops = engine->ops;
if (ops == utrace_detached_ops) {
report->detaches = true;
return NULL;
}
I think in the longer term mark_engine_detached() should not change
engine->flags at all but add QUIESCE to ->utrace_flags. However, this
breaks utrace_maybe_reap(reap => true) and we should avoid the race
with finish_callback() which clears ->reporting after report_quiesce().
A bit off-topic, but I don't think finish_callback() should check
engine->ops == &utrace_detached_ops before return. Instead we should
change finish_callback_report() to return the boolean. We shouldn't
return true without setting report->detaches.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/utrace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- kstub/kernel/utrace.c~8_fix_mark_detached_without_quiesce 2010-08-18
16:46:08.000000000 +0200
+++ kstub/kernel/utrace.c 2010-08-18 17:47:53.000000000 +0200
@@ -1522,7 +1522,7 @@ static const struct utrace_engine_ops *s
smp_rmb();
ops = engine->ops;
- if (want & UTRACE_EVENT(QUIESCE)) {
+ if ((want & UTRACE_EVENT(QUIESCE)) || ops == &utrace_detached_ops) {
if (finish_callback(task, utrace, report, engine,
(*ops->report_quiesce)(report->action,
engine, event)))
