On Thu, May 16, 2019 at 09:48:52AM +0200, Stefano Garzarella wrote: > On Wed, May 15, 2019 at 04:24:00PM +0100, Stefan Hajnoczi wrote: > > On Tue, May 07, 2019 at 02:25:43PM +0200, Stefano Garzarella wrote: > > > Hi Jorge, > > > > > > On Mon, May 06, 2019 at 01:19:55PM -0700, Jorge Moreira Broche wrote: > > > > > On Wed, May 01, 2019 at 03:08:31PM -0400, Stefan Hajnoczi wrote: > > > > > > 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 > > > > > > > Cc: "David S. Miller" > > > > > > > Cc: kvm@vger.kernel.org > > > > > > > Cc: virtualization@lists.linux-foundation.org > > > > > > > Cc: netdev@vger.kernel.org > > > > > > > Cc: kernel-team@android.com > > > > > > > Cc: stable@vger.kernel.org [4.9+] > > > > > > > Signed-off-by: Jorge E. Moreira > > > > > > > --- > > > > > > > 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? > > > > > > > > > > > > > > > > I have the same doubt. > > > > > > > > > > What do you think to take the 'the_virtio_vsock_mutex' in the > > > > > virtio_vsock_init(), keeping the previous order? > > > > > > > > > > This should prevent this issue because the virtio_vsock_probe() remains > > > > > blocked in the mutex until the end of vsock_core_init(). > > > > > > > > > > Cheers, > > > > > Stefano > > > > > > > > Hi Stefan, Stefano, > > > > Sorry for the late reply. > > > > > > Don't worry :) > > > > > > > > > > > @Stefan > > > > The order of vsock_core_exit() does not need to be changed to fix the > > > > bug I found, but not changing it means the exit function is not > > > > symmetric to the init function. > > > > > > > > @Stefano > > > > Taking the mutex from virtio_vsock_init() could work too (I haven't > > > > tried it yet), but it's unnecessary, all that needs to be done is > > > > properly initialize vsock_core before attempting to use it. > > > > > > > > I would prefer to change the order in virtio_vsock_init, while leaving > > > > virtio_vsock_exit unchanged, but I'll leave the final decision to you > > > > since I am not very familiar with the inner workings of these modules. > > > > > > In order to fix your issue, IMO changing the order in virtio_vsock_init(), > > > is enough. > > > > > > I think also that is correct to change the order in the virtio_vsock_exit(), > > > otherwise, we should have the same issue if an interrupt comes while we > > > are removing the module. > > > This should not lead to the problem that I tried to solve in 22b5c0b63f32, > > > because the vsock_core_exit() should not be called if there are open sockets, > > > since the virtio-vsock driver become the owner of AF_VSOCK protocol > > > family. There is still a race due to the interrupt handler and workqueue processing of rx packets. Imagine there are no AF_VSOCK sockets but we receive a packet from the host just as .remove() is called. We should probably cancel work/destroy the work queue immediately after resetting the virtio device. Today there is a polite flush_work() before reset, but the interrupt handler could still execute after that (and before reset) to schedule more work. Anyway, this is unrelated to this patch :). > > > > > > Not related to this patch, maybe there are some issues in the > > > virtio_vsock_probe(). I'd check better if it is correct to set > > > 'the_virtio_vsock' before the end of the initialization (e.g. spinlocks > > > are initialized later). > > > > > > Accordingly, > > > > > > Reviewed-by: Stefano Garzarella > > > > I'm going to review this once more tomorrow and investigate the > > thread-safety issues during init and exit. > > > > The core problem is that we have two sides (the virtio device and the > > network stack) that can both induce activity as soon as they are > > registered. We need to be sure that one cannot begin activity before > > the other has been fully initialized. > > I agree and maybe I found a possible issue, but it's pre-existing to this > patch: > > in the virtio_vsock_probe() we set 'the_virtio_vsock' before the end of > the initialization (e.g. 'send_pkt_list_lock' will be initialized after > this set). If between these steps the virtio_transport_send_pkt() is > called (e.g. the .stream_enqueue is called by the vsock-core), maybe > could be an issue because the spin-lock is not initialized. > > A possible solution could be to move the 'the_virtio_vsock' assignment > at the end of the probe, with a memory barrier to avoid reordering. > > Do you think we should fix this issue in this patch? (or if you prefer I can > send a separated patch) I've audited the code now. This patch improves things. It doesn't fix the pre-existing race where the_virtio_vsock is set too early during .probe(). That can be addressed in another patch by Stefano or myself. Reviewed-by: Stefan Hajnoczi