linux-kernel - Re: [PATCH 2/2] vsock: fix possible infinite sleep in vsock_connectible_wait

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Date:   Mon, 31 Oct 2022 09:43:27 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, arseny.krasnov@...persky.com,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, kys@...rosoft.com,
        haiyangz@...rosoft.com, stephen@...workplumber.org,
        wei.liu@...nel.org, linux-hyperv@...r.kernel.org
Subject: Re: [PATCH 2/2] vsock: fix possible infinite sleep in
 vsock_connectible_wait_data()

On Fri, Oct 28, 2022 at 01:56:46PM -0700, Dexuan Cui wrote:
>Currently vsock_connectible_has_data() may miss a wakeup operation
>between vsock_connectible_has_data() == 0 and the prepare_to_wait().
>
>Fix the race by adding the process to the wait qeuue before checking

s/qeuue/queue

>vsock_connectible_has_data().
>
>Fixes: b3f7fd54881b ("af_vsock: separate wait data loop")
>Signed-off-by: Dexuan Cui <decui@...rosoft.com>
>---
> net/vmw_vsock/af_vsock.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index d258fd43092e..03a6b5bc6ba7 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -1905,8 +1905,11 @@ static int vsock_connectible_wait_data(struct sock *sk,
> 	err = 0;
> 	transport = vsk->transport;
>
>-	while ((data = vsock_connectible_has_data(vsk)) == 0) {
>+	while (1) {
> 		prepare_to_wait(sk_sleep(sk), wait, TASK_INTERRUPTIBLE);
>+		data = vsock_connectible_has_data(vsk);
>+		if (data != 0)
>+			break;
>
> 		if (sk->sk_err != 0 ||
> 		    (sk->sk_shutdown & RCV_SHUTDOWN) ||
>@@ -1937,6 +1940,8 @@ static int vsock_connectible_wait_data(struct sock *sk,
> 			err = -EAGAIN;
> 			break;
> 		}
>+
>+		finish_wait(sk_sleep(sk), wait);

Since we are going to call again prepare_to_wait() on top of the loop, 
is finish_wait() call here really needed?

What about following what we do in vsock_accept and vsock_connect?

     prepare_to_wait()

     while (condition) {
         ...
         prepare_to_wait();
     }

     finish_wait()

I find it a little more readable, but your solution is fine too.

Thanks,
Stefano