Subject: [PATCH AUTOSEL 5.0 23/34] bpf: Fix preempt_enable_no_resched() abuse

From: Sasha Levin <[email-masked]>
Date: Thu, 16 May 2019 07:39:20 -0400

From: Peter Zijlstra <[email-masked]>

[ Upstream commit 0edd6b64d1939e9e9168ff27947995bb7751db5d ]

Unless the very next line is schedule(), or implies it, one must not use
preempt_enable_no_resched(). It can cause a preemption to go missing and
thereby cause arbitrary delays, breaking the PREEMPT=y invariant.

Cc: Roman Gushchin <[email-masked]>
Cc: Alexei Starovoitov <[email-masked]>
Cc: Daniel Borkmann <[email-masked]>
Signed-off-by: Peter Zijlstra (Intel) <[email-masked]>
Signed-off-by: Alexei Starovoitov <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 include/linux/bpf.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e734f163bd0b9..1fbd7672e4b37 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -455,7 +455,7 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
 		}					\
 _out:							\
 		rcu_read_unlock();			\
-		preempt_enable_no_resched();		\
+		preempt_enable();			\
 		_ret;					\
 	 })
 
-- 
2.20.1