[PATCH AUTOSEL 4.19 18/25] bpf: Fix preempt_enable_no_resched() abuse

From: Sasha Levin
Date: Thu May 16 2019 - 07:42:54 EST


From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

[ 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 <guro@xxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
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 523481a3471b5..fd95f2efe5f32 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -400,7 +400,7 @@ 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