Re: [PATCH net-next 5/5] selftests/xsk: make pkt_stream_even_odd_sequence rollback-safe

> If __pkt_stream_generate() fails midway through building per-socket
> streams, the original code overwrites xsk_arr[i].pkt_stream with a
> partial or NULL pointer before all allocations complete.
>
> Allocate all TX and RX streams into temporary arrays first and only
> assign them to xsk_arr after every allocation succeeds.  On any failure
> free the already-allocated temporaries and return -ENOMEM with no
> xsk_arr pointers modified.

Does the commit message accurately describe the problem being fixed?

The pre-patch code NULL-checked the allocation before assigning it to
xsk_arr[i].pkt_stream:

    pkt_stream = __pkt_stream_generate(pkt_stream->nb_pkts / 2,
                                       pkt_stream->pkts[0].len, i, 2);
    if (!pkt_stream)
            return -ENOMEM;
    test->ifobj_tx->xsk_arr[i].pkt_stream = pkt_stream;

so xsk_arr[i].pkt_stream would never hold a NULL pointer from a failed
allocation. __pkt_stream_generate() either returns a fully initialized
stream or NULL (it frees any partial allocations on failure), so no
"partial" pointer can exist either.

The actual bug appears to be different: when an allocation for socket i
fails, sockets 0..i-1 already have new streams installed in xsk_arr,
and both callers (testapp_xdp_shared_umem() and run_shared_umem_test())
return immediately on error without calling release_even_odd_sequence().
This leaks the already-published streams and leaves xsk_arr with a
half-replaced stream set.


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See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31554903166