Messages in this thread Patch in this message | | | Date | Mon, 24 Oct 2016 16:36:46 +0200 | From | Peter Zijlstra <> | Subject | Re: hit a KASan bug related to Perf during stress test |
| |
On Mon, Oct 24, 2016 at 03:25:55PM +0200, Oleg Nesterov wrote: > Well, if we add that PIDTYPE_TGID hack, I think we can do something > like below... > > Or do you think we should add a perf_alive() check into perf_event_pid() > for a quick fix?
That is what I was thinking. Then we don't need to do the TGID hack, I suspect some people might object to that.
> Either way it's a pity we can't report at least the valid tid, perhaps > perf_event_tid() could use task_pid_nr() if event->ns == init_pid_ns, > I dunno.
Right, but after unhash is there really still the notion of a valid TID? I mean, the TID can be reused, at which point you'll end up with two tasks etc..
But yes, very tedious.
I was thinking something like so?
---
kernel/events/core.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index c6e47e97b33f..2c9a22485e9e 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1257,7 +1257,14 @@ static u32 perf_event_pid(struct perf_event *event, struct task_struct *p) if (event->parent) event = event->parent; - return task_tgid_nr_ns(p, event->ns); + /* + * It is possible the task already got unhashed, in which case we + * cannot determine the current->group_leader/real_parent. + * + * Also, report -1 to indicate unhashed, so as not to confused with + * 0 for the idle task. + */ + return pid_alive(p) ? task_tgid_nr_ns(p, event->ns) : ~0; } static u32 perf_event_tid(struct perf_event *event, struct task_struct *p) @@ -1268,7 +1275,7 @@ static u32 perf_event_tid(struct perf_event *event, struct task_struct *p) if (event->parent) event = event->parent; - return task_pid_nr_ns(p, event->ns); + return pid_alive(p) ? task_pid_nr_ns(p, event->ns) : ~0; } /*
| |