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Date: Fri, 21 Oct 2022 15:58:56 -0700
From: Mat Martineau <mathew.j.martineau@...ux.intel.com>
To: netdev@...r.kernel.org
Cc: Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net,
kuba@...nel.org, edumazet@...gle.com, dmytro@...tyi.net,
benjamin.hesmans@...sares.net, matthieu.baerts@...sares.net,
mptcp@...ts.linux.dev,
Mat Martineau <mathew.j.martineau@...ux.intel.com>
Subject: [PATCH net 3/3] mptcp: fix abba deadlock on fastopen
From: Paolo Abeni <pabeni@...hat.com>
Our CI reported lockdep splat in the fastopen code:
======================================================
WARNING: possible circular locking dependency detected
6.0.0.mptcp_f5e8bfe9878d+ #1558 Not tainted
------------------------------------------------------
packetdrill/1071 is trying to acquire lock:
ffff8881bd198140 (sk_lock-AF_INET){+.+.}-{0:0}, at: inet_wait_for_connect+0x19c/0x310
but task is already holding lock:
ffff8881b8346540 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_sendmsg+0xfdf/0x1740
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (k-sk_lock-AF_INET){+.+.}-{0:0}:
__lock_acquire+0xb6d/0x1860
lock_acquire+0x1d8/0x620
lock_sock_nested+0x37/0xd0
inet_stream_connect+0x3f/0xa0
mptcp_connect+0x411/0x800
__inet_stream_connect+0x3ab/0x800
mptcp_stream_connect+0xac/0x110
__sys_connect+0x101/0x130
__x64_sys_connect+0x6e/0xb0
do_syscall_64+0x59/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
-> #0 (sk_lock-AF_INET){+.+.}-{0:0}:
check_prev_add+0x15e/0x2110
validate_chain+0xace/0xdf0
__lock_acquire+0xb6d/0x1860
lock_acquire+0x1d8/0x620
lock_sock_nested+0x37/0xd0
inet_wait_for_connect+0x19c/0x310
__inet_stream_connect+0x26c/0x800
tcp_sendmsg_fastopen+0x341/0x650
mptcp_sendmsg+0x109d/0x1740
sock_sendmsg+0xe1/0x120
__sys_sendto+0x1c7/0x2a0
__x64_sys_sendto+0xdc/0x1b0
do_syscall_64+0x59/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(k-sk_lock-AF_INET);
lock(sk_lock-AF_INET);
lock(k-sk_lock-AF_INET);
lock(sk_lock-AF_INET);
*** DEADLOCK ***
1 lock held by packetdrill/1071:
#0: ffff8881b8346540 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_sendmsg+0xfdf/0x1740
======================================================
The problem is caused by the blocking inet_wait_for_connect() releasing
and re-acquiring the msk socket lock while the subflow socket lock is
still held and the MPTCP socket requires that the msk socket lock must
be acquired before the subflow socket lock.
Address the issue always invoking tcp_sendmsg_fastopen() in an
unblocking manner, and later eventually complete the blocking
__inet_stream_connect() as needed.
Fixes: d98a82a6afc7 ("mptcp: handle defer connect in mptcp_sendmsg")
Reviewed-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@...sares.net>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
---
net/mptcp/protocol.c | 49 ++++++++++++++++++++++++++++++--------------
1 file changed, 34 insertions(+), 15 deletions(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index f2930699c6d3..b6dc6e260334 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1673,6 +1673,37 @@ static void mptcp_set_nospace(struct sock *sk)
set_bit(MPTCP_NOSPACE, &mptcp_sk(sk)->flags);
}
+static int mptcp_sendmsg_fastopen(struct sock *sk, struct sock *ssk, struct msghdr *msg,
+ size_t len, int *copied_syn)
+{
+ unsigned int saved_flags = msg->msg_flags;
+ struct mptcp_sock *msk = mptcp_sk(sk);
+ int ret;
+
+ lock_sock(ssk);
+ msg->msg_flags |= MSG_DONTWAIT;
+ msk->connect_flags = O_NONBLOCK;
+ msk->is_sendmsg = 1;
+ ret = tcp_sendmsg_fastopen(ssk, msg, copied_syn, len, NULL);
+ msk->is_sendmsg = 0;
+ msg->msg_flags = saved_flags;
+ release_sock(ssk);
+
+ /* do the blocking bits of inet_stream_connect outside the ssk socket lock */
+ if (ret == -EINPROGRESS && !(msg->msg_flags & MSG_DONTWAIT)) {
+ ret = __inet_stream_connect(sk->sk_socket, msg->msg_name,
+ msg->msg_namelen, msg->msg_flags, 1);
+
+ /* Keep the same behaviour of plain TCP: zero the copied bytes in
+ * case of any error, except timeout or signal
+ */
+ if (ret && ret != -EINPROGRESS && ret != -ERESTARTSYS && ret != -EINTR)
+ *copied_syn = 0;
+ }
+
+ return ret;
+}
+
static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
struct mptcp_sock *msk = mptcp_sk(sk);
@@ -1693,26 +1724,14 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
ssock = __mptcp_nmpc_socket(msk);
if (unlikely(ssock && inet_sk(ssock->sk)->defer_connect)) {
- struct sock *ssk = ssock->sk;
int copied_syn = 0;
- lock_sock(ssk);
-
- msk->connect_flags = (msg->msg_flags & MSG_DONTWAIT) ? O_NONBLOCK : 0;
- msk->is_sendmsg = 1;
- ret = tcp_sendmsg_fastopen(ssk, msg, &copied_syn, len, NULL);
- msk->is_sendmsg = 0;
+ ret = mptcp_sendmsg_fastopen(sk, ssock->sk, msg, len, &copied_syn);
copied += copied_syn;
- if (ret == -EINPROGRESS && copied_syn > 0) {
- /* reflect the new state on the MPTCP socket */
- inet_sk_state_store(sk, inet_sk_state_load(ssk));
- release_sock(ssk);
+ if (ret == -EINPROGRESS && copied_syn > 0)
goto out;
- } else if (ret) {
- release_sock(ssk);
+ else if (ret)
goto do_error;
- }
- release_sock(ssk);
}
timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
--
2.38.1
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