From: linux-hyperv-owner@vger.kernel.org
[off-list ref] On Behalf Of Stefano Garzarella
Sent: Thursday, September 26, 2019 12:48 AM

Hi Dexuan,

On Thu, Sep 26, 2019 at 01:11:27AM +0000, Dexuan Cui wrote:

quoted

...
NOTE: I only tested the code on Hyper-V. I can not test the code for
virtio socket, as I don't have a KVM host. :-( Sorry.

@Stefan, @Stefano: please review & test the patch for virtio socket,
and let me know if the patch breaks anything. Thanks!

Comment below, I'll test it ASAP!

Stefano, Thank you!

BTW, this is how I tested the patch:
1. write a socket server program in the guest. The program calls listen()
and then calls sleep(10000 seconds). Note: accept() is not called.

2. create some connections to the server program in the guest.

3. kill the server program by Ctrl+C, and "dmesg" will show the scary
call-trace, if the kernel is built with 
	CONFIG_LOCKDEP=y
	CONFIG_LOCKDEP_SUPPORT=y

4. Apply the patch, do the same test and we should no longer see the call-trace.

quoted

-		lock_sock(sk);
+		/* When "level" is 2, use the nested version to avoid the
+		 * warning "possible recursive locking detected".
+		 */
+		if (level == 1)
+			lock_sock(sk);

Since lock_sock() calls lock_sock_nested(sk, 0), could we use directly
lock_sock_nested(sk, level) with level = 0 in vsock_release() and
level = SINGLE_DEPTH_NESTING here in the while loop?

Thanks,
Stefano

IMHO it's better to make the lock usage more explicit, as the patch does.

lock_sock_nested(sk, level) or lock_sock_nested(sk, 0) seems a little
odd to me. But I'm open to your suggestion: if any of the network
maintainers, e.g. davem, also agrees with you, I'll change the code 
as you suggested. :-)

Thanks,
-- Dexuan