From: Teng Qin <qinteng@fb.com>
Date: Sat, 28 Apr 2018 23:39:29 -0700
Subject: bpf: Allow bpf_current_task_under_cgroup in interrupt
Patch-mainline: v4.18-rc1
Git-commit: 7ef3771205302a71a8bb4a2286ef98e5cade5d1a
References: bsc#1109837

Currently, the bpf_current_task_under_cgroup helper has a check where if
the BPF program is running in_interrupt(), it will return -EINVAL. This
prevents the helper to be used in many useful scenarios, particularly
BPF programs attached to Perf Events.

This commit removes the check. Tested a few NMI (Perf Event) and some
softirq context, the helper returns the correct result.

Signed-off-by: Teng Qin <qinteng@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/trace/bpf_trace.c |    2 --
 1 file changed, 2 deletions(-)

--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -454,8 +454,6 @@ BPF_CALL_2(bpf_current_task_under_cgroup
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	struct cgroup *cgrp;
 
-	if (unlikely(in_interrupt()))
-		return -EINVAL;
 	if (unlikely(idx >= array->map.max_entries))
 		return -E2BIG;