Messages in this thread | | | Date | Fri, 3 Mar 2023 15:45:18 +0300 | Subject | Re: [RFC PATCH v1] vsock: check error queue to set EPOLLERR | From | Arseniy Krasnov <> |
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On 02.03.2023 18:06, Arseniy Krasnov wrote: > > > 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." Hm, seems there is no way to reproduce it with AF_VSOCK in the current kernel: 1) I can't find test case how to use sk_error_queue(SO_TIMESTAMPXXX doesn't work on vsock - web says that it depends on NIC driver). And i don't see any generic socket layer features which uses sk_error_queue. 2) Anyway, as i mentioned above - user can't read data from sk_error_queue, because MSG_ERRQUEUE flag is not handled in af_vsock.c.
So i'll resend this patch in MSG_ZEROCOPY v2 patchset - in this case, new MSG_ZEROCOPY logic will use this patch: it will be the "reproducer"
Thanks, Arseniy > > Thanks, Arseniy >> Thanks, >> Stefano >> >>> >>> commit d021c344051af91f42c5ba9fdedc176740cbd238 >>> Author: Andy King <acking@vmware.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@google.com> >>> Date: Mon Aug 4 22:11:49 2014 -0400 >>> >>> net-timestamp: TCP timestamping >>> >>> >>>> >>>> Thanks, >>>> Stefano >>>> >>> >>> Thanks Arseniy >>> >>>>> >>>>> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.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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