Re: [PATCH net] vsock/virtio: fix potential unbounded skb queue

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, May 07, 2026 at 07:33:40AM -0700, Jakub Kicinski wrote:
>On Thu, 7 May 2026 14:59:13 +0200 Stefano Garzarella wrote:
>> >well if you want to support pathological cases such as 1 byte messages
>> >that would mean like 100x reduction no?
>>
>> Yep, but since this patch is already merged, IMHO that is better than
>> losing data in those pathological cases.
>
>We can revert if you think that the risk of regression is high..
>Please LMK soon, we can do it before patch reaches Linus.
>

Some tests in tools/testing/vsock/vsock_test.c are failing with this 
patch applied.

Test 18 are failing sometime in this way (I guess because we are 
dropping packets):

18 - SOCK_STREAM MSG_ZEROCOPY...hash mismatch

Test 22 is failing 100% in this way:

22 - SOCK_STREAM virtio credit update + SO_RCVLOWAT...send failed: 
Resource temporarily unavailable


With my followup patch adding also advertisement to the other peer 
(still draft locally, waiting for Michael proposal) I saw 22 failing, 
because tests expects that can use the entire buf_alloc, but now we are 
reducing it.  So IMO we should do like in `__sock_set_rcvbuf()` and 
double the buffer size, or at least digest an overhead equal to the 
buffer size set by the user via SO_VM_SOCKETS_BUFFER_SIZE (yeah, 
AF_VSOCK has it owns sockopt since the beginning :-().

With that approach tests are passing, but I'd like to stress a bit more 
that patch. I'll send it tomorrow as fixup of this patch, or if you 
prefer to revert, I'll send as standalone.

Thanks,
Stefano