Re: [PATCH 5.15.y] tipc: fix kernel warning when sending SYN message

[Sasha Levin]

On Wed, Apr 29, 2026 at 03:50:33PM +0800, Robert Garcia wrote:
> From: Tung Nguyen <tung.q.nguyen@xxxxxxxxxxxxxx>
>
> [ Upstream commit 11a4d6f67cf55883dc78e31c247d1903ed7feccc ]
>
> When sending a SYN message, this kernel stack trace is observed:
[...]
> It is because commit a41dad905e5a ("iov_iter: saner checks for attempt
> to copy to/from iterator") has introduced sanity check for copying
> from/to iov iterator. Lacking of copy direction from the iterator
> viewpoint would lead to kernel stack trace like above.

Thanks for the submission, but I don't think we need this in 5.15.y.

The WARN this fix silences was added by a41dad905e5a ("iov_iter: saner
checks for attempt to copy to/from iterator"), which landed in v6.1 and
has never been backported to 5.15.y. Without that prerequisite the WARN
isn't reachable in 5.15 — the SYN/ACK sends call copy_from_iter_full()
with dsz=0 on a zero-initialized msghdr, and 5.15's _copy_from_iter()
only WARNs for ITER_PIPE iters, not on data_source.

Your ITER_SOURCE -> WRITE adaptation is correct, but since the bug is
absent in 5.15 the patch isn't needed there.

--
Thanks,
Sasha