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Date:   Wed, 1 May 2019 15:08:31 -0400
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     "Jorge E. Moreira" <jemoreira@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kernel-team@...roid.com, stable@...r.kernel.org,
        sgarzare@...hat.com
Subject: Re: [PATCH] vsock/virtio: Initialize core virtio vsock before
 registering the driver

On Tue, Apr 30, 2019 at 05:30:01PM -0700, Jorge E. Moreira wrote:
> Avoid a race in which static variables in net/vmw_vsock/af_vsock.c are
> accessed (while handling interrupts) before they are initialized.
>
> 
> [    4.201410] BUG: unable to handle kernel paging request at ffffffffffffffe8
> [    4.207829] IP: vsock_addr_equals_addr+0x3/0x20
> [    4.211379] PGD 28210067 P4D 28210067 PUD 28212067 PMD 0
> [    4.211379] Oops: 0000 [#1] PREEMPT SMP PTI
> [    4.211379] Modules linked in:
> [    4.211379] CPU: 1 PID: 30 Comm: kworker/1:1 Not tainted 4.14.106-419297-gd7e28cc1f241 #1
> [    4.211379] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [    4.211379] Workqueue: virtio_vsock virtio_transport_rx_work
> [    4.211379] task: ffffa3273d175280 task.stack: ffffaea1800e8000
> [    4.211379] RIP: 0010:vsock_addr_equals_addr+0x3/0x20
> [    4.211379] RSP: 0000:ffffaea1800ebd28 EFLAGS: 00010286
> [    4.211379] RAX: 0000000000000002 RBX: 0000000000000000 RCX: ffffffffb94e42f0
> [    4.211379] RDX: 0000000000000400 RSI: ffffffffffffffe0 RDI: ffffaea1800ebdd0
> [    4.211379] RBP: ffffaea1800ebd58 R08: 0000000000000001 R09: 0000000000000001
> [    4.211379] R10: 0000000000000000 R11: ffffffffb89d5d60 R12: ffffaea1800ebdd0
> [    4.211379] R13: 00000000828cbfbf R14: 0000000000000000 R15: ffffaea1800ebdc0
> [    4.211379] FS:  0000000000000000(0000) GS:ffffa3273fd00000(0000) knlGS:0000000000000000
> [    4.211379] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    4.211379] CR2: ffffffffffffffe8 CR3: 000000002820e001 CR4: 00000000001606e0
> [    4.211379] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [    4.211379] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [    4.211379] Call Trace:
> [    4.211379]  ? vsock_find_connected_socket+0x6c/0xe0
> [    4.211379]  virtio_transport_recv_pkt+0x15f/0x740
> [    4.211379]  ? detach_buf+0x1b5/0x210
> [    4.211379]  virtio_transport_rx_work+0xb7/0x140
> [    4.211379]  process_one_work+0x1ef/0x480
> [    4.211379]  worker_thread+0x312/0x460
> [    4.211379]  kthread+0x132/0x140
> [    4.211379]  ? process_one_work+0x480/0x480
> [    4.211379]  ? kthread_destroy_worker+0xd0/0xd0
> [    4.211379]  ret_from_fork+0x35/0x40
> [    4.211379] Code: c7 47 08 00 00 00 00 66 c7 07 28 00 c7 47 08 ff ff ff ff c7 47 04 ff ff ff ff c3 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 8b 47 08 <3b> 46 08 75 0a 8b 47 04 3b 46 04 0f 94 c0 c3 31 c0 c3 90 66 2e
> [    4.211379] RIP: vsock_addr_equals_addr+0x3/0x20 RSP: ffffaea1800ebd28
> [    4.211379] CR2: ffffffffffffffe8
> [    4.211379] ---[ end trace f31cc4a2e6df3689 ]---
> [    4.211379] Kernel panic - not syncing: Fatal exception in interrupt
> [    4.211379] Kernel Offset: 0x37000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
> [    4.211379] Rebooting in 5 seconds..
> 
> Fixes: 22b5c0b63f32 ("vsock/virtio: fix kernel panic after device hot-unplug")
> Cc: Stefan Hajnoczi <stefanha@...hat.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: kvm@...r.kernel.org
> Cc: virtualization@...ts.linux-foundation.org
> Cc: netdev@...r.kernel.org
> Cc: kernel-team@...roid.com
> Cc: stable@...r.kernel.org [4.9+]
> Signed-off-by: Jorge E. Moreira <jemoreira@...gle.com>
> ---
>  net/vmw_vsock/virtio_transport.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index 15eb5d3d4750..96ab344f17bb 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -702,28 +702,27 @@ static int __init virtio_vsock_init(void)
>  	if (!virtio_vsock_workqueue)
>  		return -ENOMEM;
>  
> -	ret = register_virtio_driver(&virtio_vsock_driver);
> +	ret = vsock_core_init(&virtio_transport.transport);

Have you checked that all transport callbacks are safe even if another
CPU calls them while virtio_vsock_probe() is executing on another CPU?

>  	if (ret)
>  		goto out_wq;
>  
> -	ret = vsock_core_init(&virtio_transport.transport);
> +	ret = register_virtio_driver(&virtio_vsock_driver);
>  	if (ret)
> -		goto out_vdr;
> +		goto out_vci;
>  
>  	return 0;
>  
> -out_vdr:
> -	unregister_virtio_driver(&virtio_vsock_driver);
> +out_vci:
> +	vsock_core_exit();
>  out_wq:
>  	destroy_workqueue(virtio_vsock_workqueue);
>  	return ret;
> -
>  }
>  
>  static void __exit virtio_vsock_exit(void)
>  {
> -	vsock_core_exit();
>  	unregister_virtio_driver(&virtio_vsock_driver);
> +	vsock_core_exit();
>  	destroy_workqueue(virtio_vsock_workqueue);
>  }

The virtio_vsock_exit() order is intentional:

  commit 22b5c0b63f32568e130fa2df4ba23efce3eb495b
  Author: Stefano Garzarella <sgarzare@...hat.com>
  Date:   Fri Feb 1 12:42:06 2019 +0100

      vsock/virtio: fix kernel panic after device hot-unplug

      virtio_vsock_remove() invokes the vsock_core_exit() also if there
      are opened sockets for the AF_VSOCK protocol family. In this way
      the vsock "transport" pointer is set to NULL, triggering the
      kernel panic at the first socket activity.

      This patch move the vsock_core_init()/vsock_core_exit() in the
      virtio_vsock respectively in module_init and module_exit functions,
      that cannot be invoked until there are open sockets.

Calling vsock_core_exit() after unregister_virtio_driver() is likely to
lead to the issue that Stefano tried to fix.

Is it necessary to change virtio_vsock_exit()?

Stefan

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