On Thu, Sep 17, 2015 at 07:30:34AM -0400, Tejun Heo wrote:
>
> Maybe add that this led to a deadlock and add a Link tag to this
> thread?
I'll add a note about the deadlock but I don't like Link tags
because websites die and you can always just google the patch
subject.
> > + nlk_sk(sk)->bound = !!portid;
>
> !! isn't necessasry and this creates ordering between two stores.
!! was necessary because we're going from a u32 to a bool.
> ->bound must be visible only after ->portid is visible, so this should
> be smp_store_release().
But yes there are ordering issues here so I've decided to make
rhashtable use a new field for its hash instead.
Note that I've dropped the acks as this patch is now substantially
different.
---8<---
The commit c0bb07df7d981e4091432754e30c9c720e2c0c78 ("netlink:
Reset portid after netlink_insert failure") introduced a race
condition where if two threads try to autobind the same socket
one of them may end up with a zero port ID. This led to kernel
deadlocks that were observed by multiple people.
This patch reverts that commit and instead fixes it by introducing
a separte rhash_portid variable so that the real portid is only set
after the socket has been successfully hashed.
Fixes: c0bb07df7d98 ("netlink: Reset portid after netlink_insert failure")
Reported-by: Tejun Heo <t...@kernel.org>
Reported-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au>
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index dea9253..7157bad 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -988,7 +988,7 @@ static inline int netlink_compare(struct
rhashtable_compare_arg *arg,
const struct netlink_compare_arg *x = arg->key;
const struct netlink_sock *nlk = ptr;
- return nlk->portid != x->portid ||
+ return nlk->rhash_portid != x->portid ||
!net_eq(sock_net(&nlk->sk), read_pnet(&x->pnet));
}
@@ -1014,7 +1014,7 @@ static int __netlink_insert(struct netlink_table *table,
struct sock *sk)
{
struct netlink_compare_arg arg;
- netlink_compare_arg_init(&arg, sock_net(sk), nlk_sk(sk)->portid);
+ netlink_compare_arg_init(&arg, sock_net(sk), nlk_sk(sk)->rhash_portid);
return rhashtable_lookup_insert_key(&table->hash, &arg,
&nlk_sk(sk)->node,
netlink_rhashtable_params);
@@ -1076,17 +1076,19 @@ static int netlink_insert(struct sock *sk, u32 portid)
unlikely(atomic_read(&table->hash.nelems) >= UINT_MAX))
goto err;
- nlk_sk(sk)->portid = portid;
+ nlk_sk(sk)->rhash_portid = portid;
sock_hold(sk);
err = __netlink_insert(table, sk);
if (err) {
if (err == -EEXIST)
err = -EADDRINUSE;
- nlk_sk(sk)->portid = 0;
sock_put(sk);
+ goto err;
}
+ nlk_sk(sk)->portid = portid;
+
err:
release_sock(sk);
return err;
@@ -3197,7 +3199,7 @@ static inline u32 netlink_hash(const void *data, u32 len,
u32 seed)
const struct netlink_sock *nlk = data;
struct netlink_compare_arg arg;
- netlink_compare_arg_init(&arg, sock_net(&nlk->sk), nlk->portid);
+ netlink_compare_arg_init(&arg, sock_net(&nlk->sk), nlk->rhash_portid);
return jhash2((u32 *)&arg, netlink_compare_arg_len / sizeof(u32), seed);
}
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 8900840..c96dfa3 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -25,6 +25,7 @@ struct netlink_ring {
struct netlink_sock {
/* struct sock has to be the first member of netlink_sock */
struct sock sk;
+ u32 rhash_portid;
u32 portid;
u32 dst_portid;
u32 dst_group;
--
Email: Herbert Xu <herb...@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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