On Fri, Aug 15, 2025 at 06:44:47AM -0400, Michael S. Tsirkin wrote:

On Fri, Aug 15, 2025 at 11:09:24AM +0100, Will Deacon wrote:

quoted

On Tue, Aug 12, 2025 at 06:15:46AM -0400, Michael S. Tsirkin wrote:

quoted

On Tue, Aug 12, 2025 at 03:03:02AM -0700, syzbot wrote:

quoted

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in virtio_transport_send_pkt_info

OK so the issue triggers on
commit 6693731487a8145a9b039bc983d77edc47693855
Author: Will Deacon [off-list ref]
Date:   Thu Jul 17 10:01:16 2025 +0100

    vsock/virtio: Allocate nonlinear SKBs for handling large transmit buffers
    

but does not trigger on:

commit 8ca76151d2c8219edea82f1925a2a25907ff6a9d
Author: Will Deacon [off-list ref]
Date:   Thu Jul 17 10:01:15 2025 +0100

    vsock/virtio: Rename virtio_vsock_skb_rx_put()
    


Will, I suspect your patch merely uncovers a latent bug
in zero copy handling elsewhere.

I'm still looking at this, but I'm not sure zero-copy is the right place
to focus on.

The bisected patch 6693731487a8 ("vsock/virtio: Allocate nonlinear SKBs
for handling large transmit buffers") only has two hunks. The first is
for the non-zcopy case and the latter is a no-op for zcopy, as
skb_len == VIRTIO_VSOCK_SKB_HEADROOM and so we end up with a linear SKB
regardless.

I'll keep digging...

Will