Re: [net-next PATCH v3 4/8] net: Change return type of sk_busy_loop from bool to void
From: Christoph Paasch <hidden>
Date: 2019-03-20 18:35:45
Also in:
lkml, netdev
Hello, On Fri, Mar 24, 2017 at 3:23 PM Alexander Duyck [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Alexander Duyck <redacted>quoted
From what I can tell there is only a couple spots where we are actuallychecking the return value of sk_busy_loop. As there are only a few consumers of that data, and the data being checked for can be replaced with a check for !skb_queue_empty() we might as well just pull the code out of sk_busy_loop and place it in the spots that actually need it. Signed-off-by: Alexander Duyck <redacted> Acked-by: Eric Dumazet <edumazet@google.com> --- include/net/busy_poll.h | 5 ++--- net/core/datagram.c | 8 ++++++-- net/core/dev.c | 25 +++++++++++-------------- net/sctp/socket.c | 9 ++++++--- 4 files changed, 25 insertions(+), 22 deletions(-)diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h index b82d6ba70a14..c55760f4820f 100644 --- a/include/net/busy_poll.h +++ b/include/net/busy_poll.h@@ -74,7 +74,7 @@ static inline bool busy_loop_timeout(unsigned long end_time) return time_after(now, end_time); } -bool sk_busy_loop(struct sock *sk, int nonblock); +void sk_busy_loop(struct sock *sk, int nonblock); #else /* CONFIG_NET_RX_BUSY_POLL */ static inline unsigned long net_busy_loop_on(void)@@ -97,9 +97,8 @@ static inline bool busy_loop_timeout(unsigned long end_time) return true; } -static inline bool sk_busy_loop(struct sock *sk, int nonblock) +static inline void sk_busy_loop(struct sock *sk, int nonblock) { - return false; } #endif /* CONFIG_NET_RX_BUSY_POLL */diff --git a/net/core/datagram.c b/net/core/datagram.c index ea633342ab0d..4608aa245410 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c@@ -256,8 +256,12 @@ struct sk_buff *__skb_try_recv_datagram(struct sock *sk, unsigned int flags, } spin_unlock_irqrestore(&queue->lock, cpu_flags); - } while (sk_can_busy_loop(sk) && - sk_busy_loop(sk, flags & MSG_DONTWAIT)); + + if (!sk_can_busy_loop(sk)) + break; + + sk_busy_loop(sk, flags & MSG_DONTWAIT); + } while (!skb_queue_empty(&sk->sk_receive_queue));
since this change I am hitting stalls where it's looping in this while-loop with syzkaller. It worked prior to this change because sk->sk_napi_id was not set thus sk_busy_loop would make us get out of the loop. Now, it keeps on looping because there is an skb in the queue with skb->len == 0 and we are peeking with an offset, thus __skb_try_recv_from_queue will return NULL and thus we have no way of getting out of the loop. I'm not sure what would be the best way to fix it. I don't see why we end up with an skb in the list with skb->len == 0. So, shooting a quick e-mail, maybe somebody has an idea :-) I have the syzkaller-reproducer if needed. Thanks, Christoph
quoted hunk ↗ jump to hunk
error = -EAGAIN;diff --git a/net/core/dev.c b/net/core/dev.c index ab337bf5bbf4..af70eb6ba682 100644 --- a/net/core/dev.c +++ b/net/core/dev.c@@ -5060,21 +5060,19 @@ static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock) do_softirq(); } -bool sk_busy_loop(struct sock *sk, int nonblock) +void sk_busy_loop(struct sock *sk, int nonblock) { unsigned long end_time = !nonblock ? sk_busy_loop_end_time(sk) : 0; int (*napi_poll)(struct napi_struct *napi, int budget); void *have_poll_lock = NULL; struct napi_struct *napi; unsigned int napi_id; - int rc; restart: napi_id = READ_ONCE(sk->sk_napi_id); if (napi_id < MIN_NAPI_ID) - return 0; + return; - rc = false; napi_poll = NULL; rcu_read_lock();@@ -5085,7 +5083,8 @@ bool sk_busy_loop(struct sock *sk, int nonblock) preempt_disable(); for (;;) { - rc = 0; + int work = 0; + local_bh_disable(); if (!napi_poll) { unsigned long val = READ_ONCE(napi->state);@@ -5103,12 +5102,12 @@ bool sk_busy_loop(struct sock *sk, int nonblock) have_poll_lock = netpoll_poll_lock(napi); napi_poll = napi->poll; } - rc = napi_poll(napi, BUSY_POLL_BUDGET); - trace_napi_poll(napi, rc, BUSY_POLL_BUDGET); + work = napi_poll(napi, BUSY_POLL_BUDGET); + trace_napi_poll(napi, work, BUSY_POLL_BUDGET); count: - if (rc > 0) + if (work > 0) __NET_ADD_STATS(sock_net(sk), - LINUX_MIB_BUSYPOLLRXPACKETS, rc); + LINUX_MIB_BUSYPOLLRXPACKETS, work); local_bh_enable(); if (nonblock || !skb_queue_empty(&sk->sk_receive_queue) ||@@ -5121,9 +5120,9 @@ bool sk_busy_loop(struct sock *sk, int nonblock) preempt_enable(); rcu_read_unlock(); cond_resched(); - rc = !skb_queue_empty(&sk->sk_receive_queue); - if (rc || busy_loop_timeout(end_time)) - return rc; + if (!skb_queue_empty(&sk->sk_receive_queue) || + busy_loop_timeout(end_time)) + return; goto restart; } cpu_relax();@@ -5131,10 +5130,8 @@ bool sk_busy_loop(struct sock *sk, int nonblock) if (napi_poll) busy_poll_stop(napi, have_poll_lock); preempt_enable(); - rc = !skb_queue_empty(&sk->sk_receive_queue); out: rcu_read_unlock(); - return rc; } EXPORT_SYMBOL(sk_busy_loop);diff --git a/net/sctp/socket.c b/net/sctp/socket.c index 72cc3ecf6516..ccc08fc39722 100644 --- a/net/sctp/socket.c +++ b/net/sctp/socket.c@@ -7518,9 +7518,12 @@ struct sk_buff *sctp_skb_recv_datagram(struct sock *sk, int flags, if (sk->sk_shutdown & RCV_SHUTDOWN) break; - if (sk_can_busy_loop(sk) && - sk_busy_loop(sk, noblock)) - continue; + if (sk_can_busy_loop(sk)) { + sk_busy_loop(sk, noblock); + + if (!skb_queue_empty(&sk->sk_receive_queue)) + continue; + } /* User doesn't want to wait. */ error = -EAGAIN;