From: Paolo Abeni pabeni@redhat.com
[ Upstream commit 7d803344fdc3e38079fabcf38b1e4cb6f8faa655 ]
MatM reported a deadlock at fastopening time:
INFO: task syz-executor.0:11454 blocked for more than 143 seconds. Tainted: G S 6.1.0-rc5-03226-gdb0157db5153 #1 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:syz-executor.0 state:D stack:25104 pid:11454 ppid:424 flags:0x00004006 Call Trace: <TASK> context_switch kernel/sched/core.c:5191 [inline] __schedule+0x5c2/0x1550 kernel/sched/core.c:6503 schedule+0xe8/0x1c0 kernel/sched/core.c:6579 __lock_sock+0x142/0x260 net/core/sock.c:2896 lock_sock_nested+0xdb/0x100 net/core/sock.c:3466 __mptcp_close_ssk+0x1a3/0x790 net/mptcp/protocol.c:2328 mptcp_destroy_common+0x16a/0x650 net/mptcp/protocol.c:3171 mptcp_disconnect+0xb8/0x450 net/mptcp/protocol.c:3019 __inet_stream_connect+0x897/0xa40 net/ipv4/af_inet.c:720 tcp_sendmsg_fastopen+0x3dd/0x740 net/ipv4/tcp.c:1200 mptcp_sendmsg_fastopen net/mptcp/protocol.c:1682 [inline] mptcp_sendmsg+0x128a/0x1a50 net/mptcp/protocol.c:1721 inet6_sendmsg+0x11f/0x150 net/ipv6/af_inet6.c:663 sock_sendmsg_nosec net/socket.c:714 [inline] sock_sendmsg+0xf7/0x190 net/socket.c:734 ____sys_sendmsg+0x336/0x970 net/socket.c:2476 ___sys_sendmsg+0x122/0x1c0 net/socket.c:2530 __sys_sendmmsg+0x18d/0x460 net/socket.c:2616 __do_sys_sendmmsg net/socket.c:2645 [inline] __se_sys_sendmmsg net/socket.c:2642 [inline] __x64_sys_sendmmsg+0x9d/0x110 net/socket.c:2642 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f5920a75e7d RSP: 002b:00007f59201e8028 EFLAGS: 00000246 ORIG_RAX: 0000000000000133 RAX: ffffffffffffffda RBX: 00007f5920bb4f80 RCX: 00007f5920a75e7d RDX: 0000000000000001 RSI: 0000000020002940 RDI: 0000000000000005 RBP: 00007f5920ae7593 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000020004050 R11: 0000000000000246 R12: 0000000000000000 R13: 000000000000000b R14: 00007f5920bb4f80 R15: 00007f59201c8000 </TASK>
In the error path, tcp_sendmsg_fastopen() ends-up calling mptcp_disconnect(), and the latter tries to close each subflow, acquiring the socket lock on each of them.
At fastopen time, we have a single subflow, and such subflow socket lock is already held by the called, causing the deadlock.
We already track the 'fastopen in progress' status inside the msk socket. Use it to address the issue, making mptcp_disconnect() a no op when invoked from the fastopen (error) path and doing the relevant cleanup after releasing the subflow socket lock.
While at the above, rename the fastopen status bit to something more meaningful.
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/321 Fixes: fa9e57468aa1 ("mptcp: fix abba deadlock on fastopen") Reported-by: Mat Martineau mathew.j.martineau@linux.intel.com Reviewed-by: Mat Martineau mathew.j.martineau@linux.intel.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Mat Martineau mathew.j.martineau@linux.intel.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/mptcp/protocol.c | 18 +++++++++++++++--- net/mptcp/protocol.h | 2 +- 2 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 1dbc62537259..e64ea2ca1c7a 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -1673,6 +1673,8 @@ static void mptcp_set_nospace(struct sock *sk) set_bit(MPTCP_NOSPACE, &mptcp_sk(sk)->flags); }
+static int mptcp_disconnect(struct sock *sk, int flags); + static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msghdr *msg, size_t len, int *copied_syn) { @@ -1683,9 +1685,9 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msgh lock_sock(ssk); msg->msg_flags |= MSG_DONTWAIT; msk->connect_flags = O_NONBLOCK; - msk->is_sendmsg = 1; + msk->fastopening = 1; ret = tcp_sendmsg_fastopen(ssk, msg, copied_syn, len, NULL); - msk->is_sendmsg = 0; + msk->fastopening = 0; msg->msg_flags = saved_flags; release_sock(ssk);
@@ -1699,6 +1701,8 @@ static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msgh */ if (ret && ret != -EINPROGRESS && ret != -ERESTARTSYS && ret != -EINTR) *copied_syn = 0; + } else if (ret && ret != -EINPROGRESS) { + mptcp_disconnect(sk, 0); }
return ret; @@ -3000,6 +3004,14 @@ static int mptcp_disconnect(struct sock *sk, int flags) { struct mptcp_sock *msk = mptcp_sk(sk);
+ /* We are on the fastopen error path. We can't call straight into the + * subflows cleanup code due to lock nesting (we are already under + * msk->firstsocket lock). Do nothing and leave the cleanup to the + * caller. + */ + if (msk->fastopening) + return 0; + inet_sk_state_store(sk, TCP_CLOSE);
mptcp_stop_timer(sk); @@ -3566,7 +3578,7 @@ static int mptcp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len) /* if reaching here via the fastopen/sendmsg path, the caller already * acquired the subflow socket lock, too. */ - if (msk->is_sendmsg) + if (msk->fastopening) err = __inet_stream_connect(ssock, uaddr, addr_len, msk->connect_flags, 1); else err = inet_stream_connect(ssock, uaddr, addr_len, msk->connect_flags); diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 6a09ab99a12d..380bddbc52d4 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -286,7 +286,7 @@ struct mptcp_sock { u8 recvmsg_inq:1, cork:1, nodelay:1, - is_sendmsg:1; + fastopening:1; int connect_flags; struct work_struct work; struct sk_buff *ooo_last_skb;