perf/core: Don't report zero PIDs for exiting tasks

The exiting/dead task has no PIDs and in this case perf_event_pid/tid()
return zero, change them to return -1 to distinguish this case from
idle threads.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170822155928.GA6892@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 14 insertions, 9 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1ac5015bab04..b411321b6c26 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1249,26 +1249,31 @@ unclone_ctx(struct perf_event_context *ctx)
         return parent_ctx;
 }
 
-static u32 perf_event_pid(struct perf_event *event, struct task_struct *p)
+static u32 perf_event_pid_type(struct perf_event *event, struct task_struct *p,
+                                enum pid_type type)
 {
+        u32 nr;
         /*
          * only top level events have the pid namespace they were created in
          */
         if (event->parent)
                 event = event->parent;
 
-        return task_tgid_nr_ns(p, event->ns);
+        nr = __task_pid_nr_ns(p, type, event->ns);
+        /* avoid -1 if it is idle thread or runs in another ns */
+        if (!nr && !pid_alive(p))
+                nr = -1;
+        return nr;
 }
 
-static u32 perf_event_tid(struct perf_event *event, struct task_struct *p)
+static u32 perf_event_pid(struct perf_event *event, struct task_struct *p)
 {
-        /*
-         * only top level events have the pid namespace they were created in
-         */
-        if (event->parent)
-                event = event->parent;
+        return perf_event_pid_type(event, p, __PIDTYPE_TGID);
+}
 
-        return task_pid_nr_ns(p, event->ns);
+static u32 perf_event_tid(struct perf_event *event, struct task_struct *p)
+{
+        return perf_event_pid_type(event, p, PIDTYPE_PID);
 }
 
 /*