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SubjectRe: [PATCH net v2] vsock: Fix a lockdep warning in __vsock_release()
On Fri, Sep 27, 2019 at 05:37:20AM +0000, Dexuan Cui wrote:
> > From: linux-hyperv-owner@vger.kernel.org
> > <linux-hyperv-owner@vger.kernel.org> 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:
> > > ...
> > > 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.

Thanks very useful! I'll follow these steps!

>
> > > - 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. :-)

Sure!

Just to be clear, I'm proposing this (plus the changes in the transports
and yours useful comments):

--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -638,7 +638,7 @@ struct sock *__vsock_create(struct net *net,
}
EXPORT_SYMBOL_GPL(__vsock_create);

-static void __vsock_release(struct sock *sk)
+static void __vsock_release(struct sock *sk, int level)
{
if (sk) {
struct sk_buff *skb;
@@ -650,7 +650,7 @@ static void __vsock_release(struct sock *sk)

transport->release(vsk);

- lock_sock(sk);
+ lock_sock_nested(sk, level);
sock_orphan(sk);
sk->sk_shutdown = SHUTDOWN_MASK;

@@ -659,7 +659,7 @@ static void __vsock_release(struct sock *sk)

/* Clean up any sockets that never were accepted. */
while ((pending = vsock_dequeue_accept(sk)) != NULL) {
- __vsock_release(pending);
+ __vsock_release(pending, SINGLE_DEPTH_NESTING);
sock_put(pending);
}

@@ -708,7 +708,7 @@ EXPORT_SYMBOL_GPL(vsock_stream_has_space);

static int vsock_release(struct socket *sock)
{
- __vsock_release(sock->sk);
+ __vsock_release(sock->sk, 0);
sock->sk = NULL;
sock->state = SS_FREE;

Thanks,
Stefano
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