| Message ID | 160477791482.608263.14389359214124051944.stgit@john-XPS-13-9370 (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF |
| Headers | show |
| Series | sockmap fixes | expand |
On 11/7/20 8:38 PM, John Fastabend wrote: > If a socket redirects to itself and it is under memory pressure it is > possible to get a socket stuck so that recv() returns EAGAIN and the > socket can not advance for some time. This happens because when > redirecting a skb to the same socket we received the skb on we first > check if it is OK to enqueue the skb on the receiving socket by checking > memory limits. But, if the skb is itself the object holding the memory > needed to enqueue the skb we will keep retrying from kernel side > and always fail with EAGAIN. Then userspace will get a recv() EAGAIN > error if there are no skbs in the psock ingress queue. This will continue > until either some skbs get kfree'd causing the memory pressure to > reduce far enough that we can enqueue the pending packet or the > socket is destroyed. In some cases its possible to get a socket > stuck for a noticable amount of time if the socket is only receiving > skbs from sk_skb verdict programs. To reproduce I make the socket > memory limits ridiculously low so sockets are always under memory > pressure. More often though if under memory pressure it looks like > a spurious EAGAIN error on user space side causing userspace to retry > and typically enough has moved on the memory side that it works. > > To fix skip memory checks and skb_orphan if receiving on the same > sock as already assigned. > > For SK_PASS cases this is easy, its always the same socket so we > can just omit the orphan/set_owner pair. > > For backlog cases we need to check skb->sk and decide if the orphan > and set_owner pair are needed. > > Fixes: 51199405f9672 ("bpf: skb_verdict, support SK_PASS on RX BPF path") > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > --- > net/core/skmsg.c | 72 ++++++++++++++++++++++++++++++++++++++++-------------- > 1 file changed, 53 insertions(+), 19 deletions(-) > > diff --git a/net/core/skmsg.c b/net/core/skmsg.c > index fe44280c033e..580252e532da 100644 > --- a/net/core/skmsg.c > +++ b/net/core/skmsg.c > @@ -399,38 +399,38 @@ int sk_msg_memcopy_from_iter(struct sock *sk, struct iov_iter *from, > } > EXPORT_SYMBOL_GPL(sk_msg_memcopy_from_iter); > > -static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb) > +static struct sk_msg *sk_psock_create_ingress_msg(struct sock *sk, > + struct sk_buff *skb) > { > - struct sock *sk = psock->sk; > - int copied = 0, num_sge; > struct sk_msg *msg; > > if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) > - return -EAGAIN; > + return NULL; > + > + if (!sk_rmem_schedule(sk, skb, skb->len)) Isn't accounting always truesize based, thus we should fix & convert all skb->len to skb->truesize ? > + return NULL; > > msg = kzalloc(sizeof(*msg), __GFP_NOWARN | GFP_ATOMIC); > if (unlikely(!msg)) > - return -EAGAIN; > - if (!sk_rmem_schedule(sk, skb, skb->len)) { > - kfree(msg); > - return -EAGAIN; > - } > + return NULL; > > sk_msg_init(msg); > - num_sge = skb_to_sgvec(skb, msg->sg.data, 0, skb->len); > + return msg; > +} > +
Daniel Borkmann wrote: > On 11/7/20 8:38 PM, John Fastabend wrote: > > If a socket redirects to itself and it is under memory pressure it is > > possible to get a socket stuck so that recv() returns EAGAIN and the > > socket can not advance for some time. This happens because when > > redirecting a skb to the same socket we received the skb on we first > > check if it is OK to enqueue the skb on the receiving socket by checking > > memory limits. But, if the skb is itself the object holding the memory > > needed to enqueue the skb we will keep retrying from kernel side > > and always fail with EAGAIN. Then userspace will get a recv() EAGAIN > > error if there are no skbs in the psock ingress queue. This will continue > > until either some skbs get kfree'd causing the memory pressure to > > reduce far enough that we can enqueue the pending packet or the > > socket is destroyed. In some cases its possible to get a socket > > stuck for a noticable amount of time if the socket is only receiving > > skbs from sk_skb verdict programs. To reproduce I make the socket > > memory limits ridiculously low so sockets are always under memory > > pressure. More often though if under memory pressure it looks like > > a spurious EAGAIN error on user space side causing userspace to retry > > and typically enough has moved on the memory side that it works. > > > > To fix skip memory checks and skb_orphan if receiving on the same > > sock as already assigned. > > > > For SK_PASS cases this is easy, its always the same socket so we > > can just omit the orphan/set_owner pair. > > > > For backlog cases we need to check skb->sk and decide if the orphan > > and set_owner pair are needed. > > > > Fixes: 51199405f9672 ("bpf: skb_verdict, support SK_PASS on RX BPF path") > > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > > --- > > net/core/skmsg.c | 72 ++++++++++++++++++++++++++++++++++++++++-------------- > > 1 file changed, 53 insertions(+), 19 deletions(-) > > > > diff --git a/net/core/skmsg.c b/net/core/skmsg.c > > index fe44280c033e..580252e532da 100644 > > --- a/net/core/skmsg.c > > +++ b/net/core/skmsg.c > > @@ -399,38 +399,38 @@ int sk_msg_memcopy_from_iter(struct sock *sk, struct iov_iter *from, > > } > > EXPORT_SYMBOL_GPL(sk_msg_memcopy_from_iter); > > > > -static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb) > > +static struct sk_msg *sk_psock_create_ingress_msg(struct sock *sk, > > + struct sk_buff *skb) > > { > > - struct sock *sk = psock->sk; > > - int copied = 0, num_sge; > > struct sk_msg *msg; > > > > if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) > > - return -EAGAIN; > > + return NULL; > > + > > + if (!sk_rmem_schedule(sk, skb, skb->len)) > > Isn't accounting always truesize based, thus we should fix & convert all skb->len > to skb->truesize ? Right good catch, will fix in v2.
diff --git a/net/core/skmsg.c b/net/core/skmsg.c index fe44280c033e..580252e532da 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -399,38 +399,38 @@ int sk_msg_memcopy_from_iter(struct sock *sk, struct iov_iter *from, } EXPORT_SYMBOL_GPL(sk_msg_memcopy_from_iter); -static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb) +static struct sk_msg *sk_psock_create_ingress_msg(struct sock *sk, + struct sk_buff *skb) { - struct sock *sk = psock->sk; - int copied = 0, num_sge; struct sk_msg *msg; if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) - return -EAGAIN; + return NULL; + + if (!sk_rmem_schedule(sk, skb, skb->len)) + return NULL; msg = kzalloc(sizeof(*msg), __GFP_NOWARN | GFP_ATOMIC); if (unlikely(!msg)) - return -EAGAIN; - if (!sk_rmem_schedule(sk, skb, skb->len)) { - kfree(msg); - return -EAGAIN; - } + return NULL; sk_msg_init(msg); - num_sge = skb_to_sgvec(skb, msg->sg.data, 0, skb->len); + return msg; +} + +static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb, + struct sk_psock *psock, + struct sock *sk, + struct sk_msg *msg) +{ + int num_sge = skb_to_sgvec(skb, msg->sg.data, 0, skb->len); + int copied; + if (unlikely(num_sge < 0)) { kfree(msg); return num_sge; } - /* This will transition ownership of the data from the socket where - * the BPF program was run initiating the redirect to the socket - * we will eventually receive this data on. The data will be released - * from skb_consume found in __tcp_bpf_recvmsg() after its been copied - * into user buffers. - */ - skb_set_owner_r(skb, sk); - copied = skb->len; msg->sg.start = 0; msg->sg.size = copied; @@ -442,6 +442,40 @@ static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb) return copied; } +static int sk_psock_skb_ingress(struct sk_psock *psock, struct sk_buff *skb) +{ + struct sock *sk = psock->sk; + struct sk_msg *msg; + + msg = sk_psock_create_ingress_msg(sk, skb); + if (!msg) + return -EAGAIN; + + /* This will transition ownership of the data from the socket where + * the BPF program was run initiating the redirect to the socket + * we will eventually receive this data on. The data will be released + * from skb_consume found in __tcp_bpf_recvmsg() after its been copied + * into user buffers. + */ + skb_set_owner_r(skb, sk); + return sk_psock_skb_ingress_enqueue(skb, psock, sk, msg); +} + +/* Puts an skb on the ingress queue of the socket already assigned to the + * skb. In this case we do not need to check memory limits or skb_set_owner_r + * because the skb is already accounted for here. + */ +static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb) +{ + struct sk_msg *msg = kzalloc(sizeof(*msg), __GFP_NOWARN | GFP_ATOMIC); + struct sock *sk = psock->sk; + + if (unlikely(!msg)) + return -EAGAIN; + sk_msg_init(msg); + return sk_psock_skb_ingress_enqueue(skb, psock, sk, msg); +} + static int sk_psock_handle_skb(struct sk_psock *psock, struct sk_buff *skb, u32 off, u32 len, bool ingress) { @@ -801,7 +835,7 @@ static void sk_psock_verdict_apply(struct sk_psock *psock, * retrying later from workqueue. */ if (skb_queue_empty(&psock->ingress_skb)) { - err = sk_psock_skb_ingress(psock, skb); + err = sk_psock_skb_ingress_self(psock, skb); } if (err < 0) { skb_queue_tail(&psock->ingress_skb, skb);
If a socket redirects to itself and it is under memory pressure it is possible to get a socket stuck so that recv() returns EAGAIN and the socket can not advance for some time. This happens because when redirecting a skb to the same socket we received the skb on we first check if it is OK to enqueue the skb on the receiving socket by checking memory limits. But, if the skb is itself the object holding the memory needed to enqueue the skb we will keep retrying from kernel side and always fail with EAGAIN. Then userspace will get a recv() EAGAIN error if there are no skbs in the psock ingress queue. This will continue until either some skbs get kfree'd causing the memory pressure to reduce far enough that we can enqueue the pending packet or the socket is destroyed. In some cases its possible to get a socket stuck for a noticable amount of time if the socket is only receiving skbs from sk_skb verdict programs. To reproduce I make the socket memory limits ridiculously low so sockets are always under memory pressure. More often though if under memory pressure it looks like a spurious EAGAIN error on user space side causing userspace to retry and typically enough has moved on the memory side that it works. To fix skip memory checks and skb_orphan if receiving on the same sock as already assigned. For SK_PASS cases this is easy, its always the same socket so we can just omit the orphan/set_owner pair. For backlog cases we need to check skb->sk and decide if the orphan and set_owner pair are needed. Fixes: 51199405f9672 ("bpf: skb_verdict, support SK_PASS on RX BPF path") Signed-off-by: John Fastabend <john.fastabend@gmail.com> --- net/core/skmsg.c | 72 ++++++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 53 insertions(+), 19 deletions(-)