> -----Original Message-----
> From: Dexuan Cui <de...@microsoft.com>
> Sent: Tuesday, July 30, 2019 6:26 PM
> To: Sunil Muthuswamy <sunil...@microsoft.com>; David Miller
> <da...@davemloft.net>; net...@vger.kernel.org
> Cc: KY Srinivasan <k...@microsoft.com>; Haiyang Zhang
> <haiya...@microsoft.com>; Stephen Hemminger
> <sthem...@microsoft.com>; sas...@kernel.org; Michael Kelley
> <mikel...@microsoft.com>; linux-hyp...@vger.kernel.org; linux-
> ker...@vger.kernel.org; o...@aepfle.de; a...@canonical.com;
> jasow...@redhat.com; vkuznets <vkuzn...@redhat.com>;
> marcelo.ce...@canonical.com
> Subject: [PATCH v2 net] hv_sock: Fix hang when a connection is closed
>
>
> There is a race condition for an established connection that is being closed
> by the guest: the refcnt is 4 at the end of hvs_release() (Note: here the
> 'remove_sock' is false):
>
> 1 for the initial value;
> 1 for the sk being in the bound list;
> 1 for the sk being in the connected list;
> 1 for the delayed close_work.
>
> After hvs_release() finishes, __vsock_release() -> sock_put(sk) *may*
> decrease the refcnt to 3.
>
> Concurrently, hvs_close_connection() runs in another thread:
> calls vsock_remove_sock() to decrease the refcnt by 2;
> call sock_put() to decrease the refcnt to 0, and free the sk;
> next, the "release_sock(sk)" may hang due to use-after-free.
>
> In the above, after hvs_release() finishes, if hvs_close_connection() runs
> faster than "__vsock_release() -> sock_put(sk)", then there is not any issue,
> because at the beginning of hvs_close_connection(), the refcnt is still 4.
>
> The issue can be resolved if an extra reference is taken when the
> connection is established.
>
> Fixes: a9eeb998c28d ("hv_sock: Add support for delayed close")
> Signed-off-by: Dexuan Cui <de...@microsoft.com>
> Cc: sta...@vger.kernel.org
>
> ---
>
> Changes in v2:
> Changed the location of the sock_hold() call.
> Updated the changelog accordingly.
>
> Thanks Sunil for the suggestion!
>
>
> 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 | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/net/vmw_vsock/hyperv_transport.c
> b/net/vmw_vsock/hyperv_transport.c
> index f2084e3f7aa4..9d864ebeb7b3 100644
> --- a/net/vmw_vsock/hyperv_transport.c
> +++ b/net/vmw_vsock/hyperv_transport.c
> @@ -312,6 +312,11 @@ static void hvs_close_connection(struct vmbus_channel
> *chan)
> lock_sock(sk);
> hvs_do_close_lock_held(vsock_sk(sk), true);
> release_sock(sk);
> +
> + /* Release the refcnt for the channel that's opened in
> + * hvs_open_connection().
> + */
> + sock_put(sk);
> }
>
> static void hvs_open_connection(struct vmbus_channel *chan)
> @@ -407,6 +412,9 @@ static void hvs_open_connection(struct vmbus_channel
> *chan)
> }
>
> set_per_channel_state(chan, conn_from_host ? new : sk);
> +
> + /* This reference will be dropped by hvs_close_connection(). */
> + sock_hold(conn_from_host ? new : sk);
> vmbus_set_chn_rescind_callback(chan, hvs_close_connection);
>
> /* Set the pending send size to max packet size to always get
> --
> 2.19.1
Reviewed-by: Sunil Muthuswamy <sunil...@microsoft.com>
