On Wed, 27 Jul 2022 16:06:09 +0800 Hangyu Hua wrote: > In the case of sk->dccps_qpolicy == DCCPQ_POLICY_PRIO, dccp_qpolicy_full > will drop a skb when qpolicy is full. And the lock in dccp_sendmsg is > released before sock_alloc_send_skb and then relocked after > sock_alloc_send_skb. The following conditions may lead dccp_qpolicy_push > to add skb to an already full sk_write_queue: > > thread1--->lock > thread1--->dccp_qpolicy_full: queue is full. drop a skb This linie should say "not full"? > thread1--->unlock > thread2--->lock > thread2--->dccp_qpolicy_full: queue is not full. no need to drop. > thread2--->unlock > thread1--->lock > thread1--->dccp_qpolicy_push: add a skb. queue is full. > thread1--->unlock > thread2--->lock > thread2--->dccp_qpolicy_push: add a skb! > thread2--->unlock > > Fix this by moving dccp_qpolicy_full. > > Fixes: 871a2c16c21b ("dccp: Policy-based packet dequeueing infrastructure") This code was added in b1308dc015eb0, AFAICT. Please double check. > Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx> > --- > net/dccp/proto.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/net/dccp/proto.c b/net/dccp/proto.c > index eb8e128e43e8..1a0193823c82 100644 > --- a/net/dccp/proto.c > +++ b/net/dccp/proto.c > @@ -736,11 +736,6 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > > lock_sock(sk); > > - if (dccp_qpolicy_full(sk)) { > - rc = -EAGAIN; > - goto out_release; > - } > - > timeo = sock_sndtimeo(sk, noblock); > > /* > @@ -773,6 +768,11 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) > if (rc != 0) > goto out_discard; > > + if (dccp_qpolicy_full(sk)) { > + rc = -EAGAIN; > + goto out_discard; > + } Shouldn't this be earlier, right after relocking? Why copy the data etc. if we know the queue is full? > dccp_qpolicy_push(sk, skb); > /* > * The xmit_timer is set if the TX CCID is rate-based and will expire