netdev - [PATCH v2 net 2/3] ipv6: Add rt6_make_pcpu

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Date:	Fri, 14 Aug 2015 11:05:53 -0700
From:	Martin KaFai Lau <kafai@...com>
To:	netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
CC:	"Steinar H. Gunderson" <sgunderson@...foot.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	FB Kernel Team <kernel-team@...com>
Subject: [PATCH v2 net 2/3] ipv6: Add rt6_make_pcpu_route()

It is a prep work for fixing a potential deadlock when creating
a pcpu rt.

The current rt6_get_pcpu_route() will also create a pcpu rt if one does not
exist.  This patch moves the pcpu rt creation logic into another function,
rt6_make_pcpu_route().

Signed-off-by: Martin KaFai Lau <kafai@...com>
CC: Hannes Frederic Sowa <hannes@...essinduktion.org>
---
 net/ipv6/route.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index c95c319..0a82653 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -993,13 +993,21 @@ static struct rt6_info *ip6_rt_pcpu_alloc(struct rt6_info *rt)
 /* It should be called with read_lock_bh(&tb6_lock) acquired */
 static struct rt6_info *rt6_get_pcpu_route(struct rt6_info *rt)
 {
-	struct rt6_info *pcpu_rt, *prev, **p;
+	struct rt6_info *pcpu_rt, **p;
 
 	p = this_cpu_ptr(rt->rt6i_pcpu);
 	pcpu_rt = *p;
 
-	if (pcpu_rt)
-		goto done;
+	if (pcpu_rt) {
+		dst_hold(&pcpu_rt->dst);
+		rt6_dst_from_metrics_check(pcpu_rt);
+	}
+	return pcpu_rt;
+}
+
+static struct rt6_info *rt6_make_pcpu_route(struct rt6_info *rt)
+{
+	struct rt6_info *pcpu_rt, *prev, **p;
 
 	pcpu_rt = ip6_rt_pcpu_alloc(rt);
 	if (!pcpu_rt) {
@@ -1009,6 +1017,7 @@ static struct rt6_info *rt6_get_pcpu_route(struct rt6_info *rt)
 		goto done;
 	}
 
+	p = this_cpu_ptr(rt->rt6i_pcpu);
 	prev = cmpxchg(p, NULL, pcpu_rt);
 	if (prev) {
 		/* If someone did it before us, return prev instead */
@@ -1093,8 +1102,11 @@ redo_rt6_select:
 		rt->dst.lastuse = jiffies;
 		rt->dst.__use++;
 		pcpu_rt = rt6_get_pcpu_route(rt);
-		read_unlock_bh(&table->tb6_lock);
 
+		if (!pcpu_rt)
+			pcpu_rt = rt6_make_pcpu_route(rt);
+
+		read_unlock_bh(&table->tb6_lock);
 		return pcpu_rt;
 	}
 }
-- 
1.8.1

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