[PATCH] ipv6: get rid of ipip6_prl_lock

Eric Dumazet
2010-05-31T05:04:55Z

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@gmail.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;
}