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Date: Fri, 27 May 2011 05:27:11 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Arun Sharma <asharma@...com>, David Miller <davem@...emloft.net>
Cc: Maximilian Engelhardt <maxi@...monizer.de>,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
StuStaNet Vorstand <vorstand@...sta.mhn.de>,
Yann Dupont <Yann.Dupont@...v-nantes.fr>,
Denys Fedoryshchenko <denys@...p.net.lb>
Subject: Re: Kernel crash after using new Intel NIC (igb)
Le jeudi 26 mai 2011 à 17:09 -0700, Arun Sharma a écrit :
> On 5/26/11 3:01 PM, Eric Dumazet wrote:
>
>
> >> Yeah - using the refcnt seems better than list_empty(), but I'm not sure
> >> that your patch addresses the race above.
> >
> > It does.
>
> True. I can't find any holes in this method and it resolves the "failure
> to unlink from unused" case.
>
> Perhaps wrap the while(1) loop into its own primitive in atomic.h or use
> an existing primitive?
>
Sure, here is a formal submission I cooked.
Thanks
[PATCH] inetpeer: fix race in unused_list manipulations
Several crashes in cleanup_once() were reported in recent kernels.
Commit d6cc1d642de9 (inetpeer: various changes) added a race in
unlink_from_unused().
One way to avoid taking unused_peers.lock before doing the list_empty()
test is to catch 0->1 refcnt transitions, using full barrier atomic
operations variants (atomic_cmpxchg() and atomic_inc_return()) instead
of previous atomic_inc() and atomic_add_unless() variants.
We then call unlink_from_unused() only for the owner of the 0->1
transition.
Add a new atomic_add_unless_return() static helper
With help from Arun Sharma.
Refs: https://bugzilla.kernel.org/show_bug.cgi?id=32772
Reported-by: Arun Sharma <asharma@...com>
Reported-by: Maximilian Engelhardt <maxi@...monizer.de>
Reported-by: Yann Dupont <Yann.Dupont@...v-nantes.fr>
Reported-by: Denys Fedoryshchenko <denys@...p.net.lb>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
net/ipv4/inetpeer.c | 42 +++++++++++++++++++++++++++---------------
1 files changed, 27 insertions(+), 15 deletions(-)
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index 9df4e63..ce616d9 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -154,11 +154,9 @@ void __init inet_initpeers(void)
/* Called with or without local BH being disabled. */
static void unlink_from_unused(struct inet_peer *p)
{
- if (!list_empty(&p->unused)) {
- spin_lock_bh(&unused_peers.lock);
- list_del_init(&p->unused);
- spin_unlock_bh(&unused_peers.lock);
- }
+ spin_lock_bh(&unused_peers.lock);
+ list_del_init(&p->unused);
+ spin_unlock_bh(&unused_peers.lock);
}
static int addr_compare(const struct inetpeer_addr *a,
@@ -205,6 +203,20 @@ static int addr_compare(const struct inetpeer_addr *a,
u; \
})
+static bool atomic_add_unless_return(atomic_t *ptr, int a, int u, int *newv)
+{
+ int cur, old = atomic_read(ptr);
+
+ while (old != u) {
+ *newv = old + a;
+ cur = atomic_cmpxchg(ptr, old, *newv);
+ if (cur == old)
+ return true;
+ old = cur;
+ }
+ return false;
+}
+
/*
* Called with rcu_read_lock()
* Because we hold no lock against a writer, its quite possible we fall
@@ -213,7 +225,8 @@ static int addr_compare(const struct inetpeer_addr *a,
* We exit from this function if number of links exceeds PEER_MAXDEPTH
*/
static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
- struct inet_peer_base *base)
+ struct inet_peer_base *base,
+ int *newrefcnt)
{
struct inet_peer *u = rcu_dereference(base->root);
int count = 0;
@@ -226,7 +239,7 @@ static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
* distinction between an unused entry (refcnt=0) and
* a freed one.
*/
- if (unlikely(!atomic_add_unless(&u->refcnt, 1, -1)))
+ if (!atomic_add_unless_return(&u->refcnt, 1, -1, newrefcnt))
u = NULL;
return u;
}
@@ -465,22 +478,23 @@ struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
struct inet_peer_base *base = family_to_base(daddr->family);
struct inet_peer *p;
unsigned int sequence;
- int invalidated;
+ int invalidated, newrefcnt = 0;
/* Look up for the address quickly, lockless.
* Because of a concurrent writer, we might not find an existing entry.
*/
rcu_read_lock();
sequence = read_seqbegin(&base->lock);
- p = lookup_rcu(daddr, base);
+ p = lookup_rcu(daddr, base, &newrefcnt);
invalidated = read_seqretry(&base->lock, sequence);
rcu_read_unlock();
if (p) {
- /* The existing node has been found.
+found: /* The existing node has been found.
* Remove the entry from unused list if it was there.
*/
- unlink_from_unused(p);
+ if (newrefcnt == 1)
+ unlink_from_unused(p);
return p;
}
@@ -494,11 +508,9 @@ struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
write_seqlock_bh(&base->lock);
p = lookup(daddr, stack, base);
if (p != peer_avl_empty) {
- atomic_inc(&p->refcnt);
+ newrefcnt = atomic_inc_return(&p->refcnt);
write_sequnlock_bh(&base->lock);
- /* Remove the entry from unused list if it was there. */
- unlink_from_unused(p);
- return p;
+ goto found;
}
p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
if (p) {
--
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