> -----Original Message-----
> From: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Sent: Sunday, July 28, 2019 11:32 AM
> To: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx>; David Miller <davem@xxxxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
> Cc: KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; Stephen Hemminger
> <sthemmin@xxxxxxxxxxxxx>; sashal@xxxxxxxxxx; Michael Kelley <mikelley@xxxxxxxxxxxxx>; linux-hyperv@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; jasowang@xxxxxxxxxx; vkuznets <vkuznets@xxxxxxxxxx>;
> marcelo.cerri@xxxxxxxxxxxxx
> Subject: [PATCH net] hv_sock: Fix hang when a connection is closed
>
>
> hvs_do_close_lock_held() may decrease the reference count to 0 and free the
> sk struct completely, and then the following release_sock(sk) may hang.
>
> Fixes: a9eeb998c28d ("hv_sock: Add support for delayed close")
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
>
> ---
> With the proper kernel debugging options enabled, first a warning can
> appear:
>
> kworker/1:0/4467 is freeing memory ..., with a lock still held there!
> stack backtrace:
> Workqueue: events vmbus_onmessage_work [hv_vmbus]
> Call Trace:
> dump_stack+0x67/0x90
> debug_check_no_locks_freed.cold.52+0x78/0x7d
> slab_free_freelist_hook+0x85/0x140
> kmem_cache_free+0xa5/0x380
> __sk_destruct+0x150/0x260
> hvs_close_connection+0x24/0x30 [hv_sock]
> vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
> process_one_work+0x241/0x600
> worker_thread+0x3c/0x390
> kthread+0x11b/0x140
> ret_from_fork+0x24/0x30
>
> and then the following release_sock(sk) can hang:
>
> watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kworker/1:0:4467]
> ...
> irq event stamp: 62890
> CPU: 1 PID: 4467 Comm: kworker/1:0 Tainted: G W 5.2.0+ #39
> Workqueue: events vmbus_onmessage_work [hv_vmbus]
> RIP: 0010:queued_spin_lock_slowpath+0x2b/0x1e0
> ...
> Call Trace:
> do_raw_spin_lock+0xab/0xb0
> release_sock+0x19/0xb0
> vmbus_onmessage_work+0x1d/0x30 [hv_vmbus]
> process_one_work+0x241/0x600
> worker_thread+0x3c/0x390
> kthread+0x11b/0x140
> ret_from_fork+0x24/0x30
>
> net/vmw_vsock/hyperv_transport.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
> index f2084e3f7aa4..efbda8ef1eff 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -309,9 +309,16 @@ static void hvs_close_connection(struct vmbus_channel *chan)
> {
> struct sock *sk = get_per_channel_state(chan);
>
> + /* Grab an extra reference since hvs_do_close_lock_held() may decrease
> + * the reference count to 0 by calling sock_put(sk).
> + */
> + sock_hold(sk);
> +
To me, it seems like when 'hvs_close_connection' is called, there should always be
an outstanding reference to the socket. The reference that is dropped by
' hvs_do_close_lock_held' is a legitimate reference that was taken by 'hvs_close_lock_held'.
Or, in other words, I think the right solution is to always maintain a reference to socket
until this routine is called and drop that here. That can be done by taking the reference to
the socket prior to ' vmbus_set_chn_rescind_callback(chan, hvs_close_connection)' and
dropping that reference at the end of 'hvs_close_connection'.
> lock_sock(sk);
> hvs_do_close_lock_held(vsock_sk(sk), true);
> release_sock(sk);
> +
> + sock_put(sk);
> }
>
> static void hvs_open_connection(struct vmbus_channel *chan)
> --
> 2.19.1
Thanks for taking a look at this. We should queue this fix and the other hvsocket fixes
for the stable branch.
