From: Duoming Zhou duoming@zju.edu.cn
[ Upstream commit 219b51a6f040fa5367adadd7d58c4dda0896a01d ]
The skb_recv_datagram() in ax25_recvmsg() will hold lock_sock and block until it receives a packet from the remote. If the client doesn`t connect to server and calls read() directly, it will not receive any packets forever. As a result, the deadlock will happen.
The fail log caused by deadlock is shown below:
[ 369.606973] INFO: task ax25_deadlock:157 blocked for more than 245 seconds. [ 369.608919] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 369.613058] Call Trace: [ 369.613315] <TASK> [ 369.614072] __schedule+0x2f9/0xb20 [ 369.615029] schedule+0x49/0xb0 [ 369.615734] __lock_sock+0x92/0x100 [ 369.616763] ? destroy_sched_domains_rcu+0x20/0x20 [ 369.617941] lock_sock_nested+0x6e/0x70 [ 369.618809] ax25_bind+0xaa/0x210 [ 369.619736] __sys_bind+0xca/0xf0 [ 369.620039] ? do_futex+0xae/0x1b0 [ 369.620387] ? __x64_sys_futex+0x7c/0x1c0 [ 369.620601] ? fpregs_assert_state_consistent+0x19/0x40 [ 369.620613] __x64_sys_bind+0x11/0x20 [ 369.621791] do_syscall_64+0x3b/0x90 [ 369.622423] entry_SYSCALL_64_after_hwframe+0x46/0xb0 [ 369.623319] RIP: 0033:0x7f43c8aa8af7 [ 369.624301] RSP: 002b:00007f43c8197ef8 EFLAGS: 00000246 ORIG_RAX: 0000000000000031 [ 369.625756] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f43c8aa8af7 [ 369.626724] RDX: 0000000000000010 RSI: 000055768e2021d0 RDI: 0000000000000005 [ 369.628569] RBP: 00007f43c8197f00 R08: 0000000000000011 R09: 00007f43c8198700 [ 369.630208] R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff845e6afe [ 369.632240] R13: 00007fff845e6aff R14: 00007f43c8197fc0 R15: 00007f43c8198700
This patch replaces skb_recv_datagram() with an open-coded variant of it releasing the socket lock before the __skb_wait_for_more_packets() call and re-acquiring it after such call in order that other functions that need socket lock could be executed.
what's more, the socket lock will be released only when recvmsg() will block and that should produce nicer overall behavior.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Suggested-by: Thomas Osterried thomas@osterried.de Signed-off-by: Duoming Zhou duoming@zju.edu.cn Reported-by: Thomas Habets <thomas@@habets.se> Acked-by: Paolo Abeni pabeni@redhat.com Reviewed-by: Eric Dumazet edumazet@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/ax25/af_ax25.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c index 7b69503dc46a..f99ed1eddf5e 100644 --- a/net/ax25/af_ax25.c +++ b/net/ax25/af_ax25.c @@ -1654,9 +1654,12 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, int flags) { struct sock *sk = sock->sk; - struct sk_buff *skb; + struct sk_buff *skb, *last; + struct sk_buff_head *sk_queue; int copied; int err = 0; + int off = 0; + long timeo;
lock_sock(sk); /* @@ -1668,11 +1671,29 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, goto out; }
- /* Now we can treat all alike */ - skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT, - flags & MSG_DONTWAIT, &err); - if (skb == NULL) - goto out; + /* We need support for non-blocking reads. */ + sk_queue = &sk->sk_receive_queue; + skb = __skb_try_recv_datagram(sk, sk_queue, flags, &off, &err, &last); + /* If no packet is available, release_sock(sk) and try again. */ + if (!skb) { + if (err != -EAGAIN) + goto out; + release_sock(sk); + timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); + while (timeo && !__skb_wait_for_more_packets(sk, sk_queue, &err, + &timeo, last)) { + skb = __skb_try_recv_datagram(sk, sk_queue, flags, &off, + &err, &last); + if (skb) + break; + + if (err != -EAGAIN) + goto done; + } + if (!skb) + goto done; + lock_sock(sk); + }
if (!sk_to_ax25(sk)->pidincl) skb_pull(skb, 1); /* Remove PID */ @@ -1719,6 +1740,7 @@ static int ax25_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, out: release_sock(sk);
+done: return err; }