netdev - [PATCH] ipv6: get rid of ipip6_prl

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Date:	Mon, 31 May 2010 07:04:55 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Julia Lawall <julia@...u.dk>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH] ipv6: get rid of ipip6_prl_lock

Le dimanche 30 mai 2010 à 23:09 +0200, Julia Lawall a écrit :
> On Sun, 30 May 2010, Eric Dumazet wrote:
> 
> > Le dimanche 30 mai 2010 à 22:50 +0200, Julia Lawall a écrit :
> > 
> > > I think the proposed patch does not work, because the for loop overwrites 
> > > p.  That use of p looks like it is completely local to the for loop, so 
> > > perhaps a new variable p1 could be added to be used there?
> > 
> > Please do so.
> > 
> > I just wanted to tell you changing GFP_KERNEL to GFP_ATOMIC is not an
> > appropriate way to solve this kind of problems. My patch was to get an
> > idea, not a full and tested patch :)
> 
> Looking at it again, there is still a problem, because in the original 
> code, the loop:
> 
...
> 
> could exit with success without the kzalloc ever being called.  If the 
> kzalloc is moved up, it could fail and then it returns immediately without 
> executing the loop.  A solution could be to leave the NULL test on p where 
> it is, and only move up the kzalloc.  Or perhaps the change in behavior 
> doesn't matter?
> 


[PATCH] ipv6: get rid of ipip6_prl_lock

As noticed by Julia Lawall, ipip6_tunnel_add_prl() incorrectly calls 
kzallloc(..., GFP_KERNEL) while a spinlock is held. He provided
a patch to use GFP_ATOMIC instead.

One possibility would be to convert this spinlock to a mutex, or
preallocate the thing before taking the lock.

After RCU conversion, it appears we dont need this lock, since 
caller already holds RTNL

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 net/ipv6/sit.c |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index e51e650..702c532 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -249,8 +249,6 @@ failed:
 	return NULL;
 }
 
-static DEFINE_SPINLOCK(ipip6_prl_lock);
-
 #define for_each_prl_rcu(start)			\
 	for (prl = rcu_dereference(start);	\
 	     prl;				\
@@ -340,7 +338,7 @@ ipip6_tunnel_add_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a, int chg)
 	if (a->addr == htonl(INADDR_ANY))
 		return -EINVAL;
 
-	spin_lock(&ipip6_prl_lock);
+	ASSERT_RTNL();
 
 	for (p = t->prl; p; p = p->next) {
 		if (p->addr == a->addr) {
@@ -370,7 +368,6 @@ ipip6_tunnel_add_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a, int chg)
 	t->prl_count++;
 	rcu_assign_pointer(t->prl, p);
 out:
-	spin_unlock(&ipip6_prl_lock);
 	return err;
 }
 
@@ -397,7 +394,7 @@ ipip6_tunnel_del_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a)
 	struct ip_tunnel_prl_entry *x, **p;
 	int err = 0;
 
-	spin_lock(&ipip6_prl_lock);
+	ASSERT_RTNL();
 
 	if (a && a->addr != htonl(INADDR_ANY)) {
 		for (p = &t->prl; *p; p = &(*p)->next) {
@@ -419,7 +416,6 @@ ipip6_tunnel_del_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a)
 		}
 	}
 out:
-	spin_unlock(&ipip6_prl_lock);
 	return err;
 }
 


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