linux-kernel - [PATCH 4.19 022/131] net: use correct this_cpu primitive in dev_recursion

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Date:   Mon, 29 Jun 2020 11:33:13 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Florian Westphal <fw@...len.de>,
        syzbot+51471b4aae195285a4a3@...kaller.appspotmail.com,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH 4.19 022/131] net: use correct this_cpu primitive in dev_recursion_level

From: Florian Westphal <fw@...len.de>

commit 28b05b92886871bdd8e6a9df73e3a15845fe8ef4 upstream.

syzbot reports:
BUG: using __this_cpu_read() in preemptible code:
caller is dev_recursion_level include/linux/netdevice.h:3052 [inline]
 __this_cpu_preempt_check+0x246/0x270 lib/smp_processor_id.c:47
 dev_recursion_level include/linux/netdevice.h:3052 [inline]
 ip6_skb_dst_mtu include/net/ip6_route.h:245 [inline]

I erronously downgraded a this_cpu_read to __this_cpu_read when
moving dev_recursion_level() around.

Reported-by: syzbot+51471b4aae195285a4a3@...kaller.appspotmail.com
Fixes: 97cdcf37b57e ("net: place xmit recursion in softnet data")
Signed-off-by: Florian Westphal <fw@...len.de>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/linux/netdevice.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 41beebcc61f45..85dc3497c74f1 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3001,7 +3001,7 @@ DECLARE_PER_CPU_ALIGNED(struct softnet_data, softnet_data);
 
 static inline int dev_recursion_level(void)
 {
-	return __this_cpu_read(softnet_data.xmit.recursion);
+	return this_cpu_read(softnet_data.xmit.recursion);
 }
 
 #define XMIT_RECURSION_LIMIT	10
-- 
2.25.1