linux-kernel - [PATCH 5.0 122/139] bpf: Fix preempt_enable_no

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Message-Id: <20190523181735.408177139@linuxfoundation.org>
Date:   Thu, 23 May 2019 21:06:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Roman Gushchin <guro@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.0 122/139] bpf: Fix preempt_enable_no_resched() abuse

[ 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@...com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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