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Date: Thu, 2 Mar 2023 18:06:19 +0300 From: Arseniy Krasnov <avkrasnov@...rdevices.ru> To: Stefano Garzarella <sgarzare@...hat.com> CC: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, <oxffffaa@...il.com>, <kernel@...rdevices.ru>, <virtualization@...ts.linux-foundation.org>, <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Bobby Eshleman <bobby.eshleman@...edance.com> Subject: Re: [RFC PATCH v1] vsock: check error queue to set EPOLLERR On 02.03.2023 16:38, Stefano Garzarella wrote: > On Thu, Mar 02, 2023 at 02:41:29PM +0300, Arseniy Krasnov wrote: >> Hello! >> >> On 02.03.2023 13:06, Stefano Garzarella wrote: >>> On Wed, Mar 01, 2023 at 08:19:45AM +0300, Arseniy Krasnov wrote: >>>> EPOLLERR must be set not only when there is error on the socket, but also >>>> when error queue of it is not empty (may be it contains some control >>>> messages). Without this patch 'poll()' won't detect data in error queue. >>> >>> Do you have a reproducer? >>> >> Dedicated reproducer - no:) >> To reproduce this issue, i used last MSG_ZEROCOPY patches. Completion was inserted to >> error queue, and 'poll()' didn't report about it. That was the reason, why this patch >> was included to MSG_ZEROCOPY patchset. But also i think it is better to reduce number >> of patches in it(i'm working on v2), so it is good to handle this patch separately. > > Yep, absolutely! > >> May be one way to reproduce it is use SO_TIMESTAMP(time info about skbuff will be queued >> to the error queue). IIUC this feature is implemented at socket layer and may work in >> vsock (but i'm not sure). Ok, i'll check it and try to implement reproducer. >> >> IIUC, for future, policy for fixes is "for each fix implement reproducer in vsock_test"? > > Nope, but for each fix we should have a Fixes tag. > > Usually we use vsock_test to check regressions on features and also the > behaviour of different transports. > My question was more about whether this problem was there before > supporting sk_buff or not, to figure out which Fixes tag to use. > Ok i see >> >>>> This patch is based on 'tcp_poll()'. >>> >>> LGTM but we should add a Fixes tag. >>> It's not clear to me whether the problem depends on when we switched to using sk_buff or was pre-existing. >>> >>> Do you have any idea when we introduced this issue? >> git blame shows, that this code exists since first commit to vsock: > > Okay, but did we use sk_error_queue before supporting sk_buff? > No I think, sk_error_queue was unavailable to user(and still unavailable today), because we don't have check for MSG_ERRQUEUE flag in recv logic in af_vsock.c (i've added it in MSG_ZEROCOPY). So even if some subsystem of the kernel inserts skb to sk_error_queue in AF_VSOCK case, user won't dequeue it. > Anyway, if we are not sure I think we can use the following Fixes tag, > I don't see any issue if we backport this patch also before supporting > sk_buff. > Ok, i'll try to prepare reproducer(may be in vsock_test) and add Fixes tag with the commit "VSOCK: Introduce VM Sockets." Thanks, Arseniy > Thanks, > Stefano > >> >> commit d021c344051af91f42c5ba9fdedc176740cbd238 >> Author: Andy King <acking@...are.com> >> Date: Wed Feb 6 14:23:56 2013 +0000 >> >> VSOCK: Introduce VM Sockets >> >> For TCP same logic was added by: >> >> commit 4ed2d765dfaccff5ebdac68e2064b59125033a3b >> Author: Willem de Bruijn <willemb@...gle.com> >> Date: Mon Aug 4 22:11:49 2014 -0400 >> >> net-timestamp: TCP timestamping >> >> >>> >>> Thanks, >>> Stefano >>> >> >> Thanks Arseniy >> >>>> >>>> Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru> >>>> --- >>>> net/vmw_vsock/af_vsock.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c >>>> index 19aea7cba26e..b5e51ef4a74c 100644 >>>> --- a/net/vmw_vsock/af_vsock.c >>>> +++ b/net/vmw_vsock/af_vsock.c >>>> @@ -1026,7 +1026,7 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock, >>>> poll_wait(file, sk_sleep(sk), wait); >>>> mask = 0; >>>> >>>> - if (sk->sk_err) >>>> + if (sk->sk_err || !skb_queue_empty_lockless(&sk->sk_error_queue)) >>>> /* Signify that there has been an error on this socket. */ >>>> mask |= EPOLLERR; >>>> >>>> -- >>>> 2.25.1 >>>> >>> >> >
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