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author | 2022-12-20 11:52:15 -0800 | |
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committer | 2022-12-21 18:05:47 -0800 | |
commit | fec3adfd754ccc99a7230e8ab9f105b65fb07bcc (patch) | |
tree | 700c8c2147933deb7f63f0bc6d40fa0bd7da41f0 /net/mptcp/subflow.c | |
parent | mptcp: fix deadlock in fastopen error path (diff) | |
download | linux-fec3adfd754ccc99a7230e8ab9f105b65fb07bcc.tar.gz linux-fec3adfd754ccc99a7230e8ab9f105b65fb07bcc.tar.bz2 linux-fec3adfd754ccc99a7230e8ab9f105b65fb07bcc.zip |
mptcp: fix lockdep false positive
MattB reported a lockdep splat in the mptcp listener code cleanup:
WARNING: possible circular locking dependency detected
packetdrill/14278 is trying to acquire lock:
ffff888017d868f0 ((work_completion)(&msk->work)){+.+.}-{0:0}, at: __flush_work (kernel/workqueue.c:3069)
but task is already holding lock:
ffff888017d84130 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_close (net/mptcp/protocol.c:2973)
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (sk_lock-AF_INET){+.+.}-{0:0}:
__lock_acquire (kernel/locking/lockdep.c:5055)
lock_acquire (kernel/locking/lockdep.c:466)
lock_sock_nested (net/core/sock.c:3463)
mptcp_worker (net/mptcp/protocol.c:2614)
process_one_work (kernel/workqueue.c:2294)
worker_thread (include/linux/list.h:292)
kthread (kernel/kthread.c:376)
ret_from_fork (arch/x86/entry/entry_64.S:312)
-> #0 ((work_completion)(&msk->work)){+.+.}-{0:0}:
check_prev_add (kernel/locking/lockdep.c:3098)
validate_chain (kernel/locking/lockdep.c:3217)
__lock_acquire (kernel/locking/lockdep.c:5055)
lock_acquire (kernel/locking/lockdep.c:466)
__flush_work (kernel/workqueue.c:3070)
__cancel_work_timer (kernel/workqueue.c:3160)
mptcp_cancel_work (net/mptcp/protocol.c:2758)
mptcp_subflow_queue_clean (net/mptcp/subflow.c:1817)
__mptcp_close_ssk (net/mptcp/protocol.c:2363)
mptcp_destroy_common (net/mptcp/protocol.c:3170)
mptcp_destroy (include/net/sock.h:1495)
__mptcp_destroy_sock (net/mptcp/protocol.c:2886)
__mptcp_close (net/mptcp/protocol.c:2959)
mptcp_close (net/mptcp/protocol.c:2974)
inet_release (net/ipv4/af_inet.c:432)
__sock_release (net/socket.c:651)
sock_close (net/socket.c:1367)
__fput (fs/file_table.c:320)
task_work_run (kernel/task_work.c:181 (discriminator 1))
exit_to_user_mode_prepare (include/linux/resume_user_mode.h:49)
syscall_exit_to_user_mode (kernel/entry/common.c:130)
do_syscall_64 (arch/x86/entry/common.c:87)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(sk_lock-AF_INET);
lock((work_completion)(&msk->work));
lock(sk_lock-AF_INET);
lock((work_completion)(&msk->work));
*** DEADLOCK ***
The report is actually a false positive, since the only existing lock
nesting is the msk socket lock acquired by the mptcp work.
cancel_work_sync() is invoked without the relevant socket lock being
held, but under a different (the msk listener) socket lock.
We could silence the splat adding a per workqueue dynamic lockdep key,
but that looks overkill. Instead just tell lockdep the msk socket lock
is not held around cancel_work_sync().
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/322
Fixes: 30e51b923e43 ("mptcp: fix unreleased socket in accept queue")
Reported-by: Matthieu Baerts <matthieu.baerts@tessares.net>
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>
Diffstat (limited to 'net/mptcp/subflow.c')
-rw-r--r-- | net/mptcp/subflow.c | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index d1d32a66ae3f..bd387d4b5a38 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1791,7 +1791,7 @@ static void subflow_state_change(struct sock *sk) } } -void mptcp_subflow_queue_clean(struct sock *listener_ssk) +void mptcp_subflow_queue_clean(struct sock *listener_sk, struct sock *listener_ssk) { struct request_sock_queue *queue = &inet_csk(listener_ssk)->icsk_accept_queue; struct mptcp_sock *msk, *next, *head = NULL; @@ -1840,8 +1840,23 @@ void mptcp_subflow_queue_clean(struct sock *listener_ssk) do_cancel_work = __mptcp_close(sk, 0); release_sock(sk); - if (do_cancel_work) + if (do_cancel_work) { + /* lockdep will report a false positive ABBA deadlock + * between cancel_work_sync and the listener socket. + * The involved locks belong to different sockets WRT + * the existing AB chain. + * Using a per socket key is problematic as key + * deregistration requires process context and must be + * performed at socket disposal time, in atomic + * context. + * Just tell lockdep to consider the listener socket + * released here. + */ + mutex_release(&listener_sk->sk_lock.dep_map, _RET_IP_); mptcp_cancel_work(sk); + mutex_acquire(&listener_sk->sk_lock.dep_map, + SINGLE_DEPTH_NESTING, 0, _RET_IP_); + } sock_put(sk); } |