Messages in this thread Patch in this message |  | | From | Jason Xing <> | Date | Mon, 16 Jan 2023 10:24:05 +0800 | Subject | Re: [PATCH v2 net] tcp: avoid the lookup process failing to get sk in ehash table |
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On Mon, Jan 16, 2023 at 8:36 AM Jason Xing <kerneljasonxing@gmail.com> wrote: > > On Mon, Jan 16, 2023 at 12:12 AM Eric Dumazet <edumazet@google.com> wrote: > > > > On Sat, Jan 14, 2023 at 2:27 PM Jason Xing <kerneljasonxing@gmail.com> wrote: > > > > > > From: Jason Xing <kernelxing@tencent.com> > > > > > > > > > Fixes: 5e0724d027f0 ("tcp/dccp: fix hashdance race for passive sessions") > > > Suggested-by: Eric Dumazet <edumazet@google.com> > > > Signed-off-by: Jason Xing <kernelxing@tencent.com> > > > Link: https://lore.kernel.org/lkml/20230112065336.41034-1-kerneljasonxing@gmail.com/ > > > --- > > > v2: > > > 1) adding the sk node into the tail of list to prevent the race. > > > 2) fix the race condition when handling time-wait socket hashdance. > > > --- > > > net/ipv4/inet_hashtables.c | 10 ++++++++++ > > > net/ipv4/inet_timewait_sock.c | 6 +++--- > > > 2 files changed, 13 insertions(+), 3 deletions(-) > > > > > > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c > > > index 24a38b56fab9..b0b54ad55507 100644 > > > --- a/net/ipv4/inet_hashtables.c > > > +++ b/net/ipv4/inet_hashtables.c > > > @@ -650,7 +650,16 @@ bool inet_ehash_insert(struct sock *sk, struct sock *osk, bool *found_dup_sk) > > > spin_lock(lock); > > > if (osk) { > > > WARN_ON_ONCE(sk->sk_hash != osk->sk_hash); > > > + if (sk_hashed(osk)) > > > > > > nit: this should be: > > > > if (sk_hashed(osk)) { [1] > > /* multi-line .... > > * .... comment. > > */ > > ret = sk_nulls_del_node_init_rcu(osk); > > goto unlock; > > }
Well, after I dug into this part, I found something as below. If we enter into the 'if (osk) {', we should always skip the next if-statement which is 'if (found_dup_sk) {' and return a proper value depending on if the osk is hashed. However, the code as above would leave variable @ret to be true if the sk_hashed(osk) returned false, then It would not go to unlock and then add the node to the list and at last return true which is unexpected.
> > if (found_dup_sk) { [2] > > > > 1) parentheses needed in [1]
> > 2) No else if in [2], since you added a "goto unlock;"
I think this modification is fine and makes the code clearer.
Thanks, Jason
> > > > I'll do that. It looks much better. > > Thanks, > Jason > > > > + /* Before deleting the node, we insert a new one to make > > > + * sure that the look-up-sk process would not miss either > > > + * of them and that at least one node would exist in ehash > > > + * table all the time. Otherwise there's a tiny chance > > > + * that lookup process could find nothing in ehash table. > > > + */ > > > + __sk_nulls_add_node_tail_rcu(sk, list); > > > ret = sk_nulls_del_node_init_rcu(osk); > > > + goto unlock; > > > } else if (found_dup_sk) { > > > *found_dup_sk = inet_ehash_lookup_by_sk(sk, list); > > > if (*found_dup_sk) > > > @@ -660,6 +669,7 @@ bool inet_ehash_insert(struct sock *sk, struct sock *osk, bool *found_dup_sk) > > > if (ret) > > > __sk_nulls_add_node_rcu(sk, list); > > > > > > +unlock: > > > spin_unlock(lock); > > > > Thanks.
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