[PATCH COMMITTED] resolv: Serialize processing in resolv/tst-resolv-txnid-collision

[Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>]

When switching name servers, response processing by two server
threads clobbers the global test state.  (There is still some
risk that this test is negatively impact by packet drops and
packet reordering, but this applies to many of the resolver tests
and is difficult to avoid.)

Fixes commit f1f00c072138af90ae6da180f260111f09afe7a3 ("resolv:
Handle transaction ID collisions in parallel queries (bug 26600)").

---
 resolv/tst-resolv-txnid-collision.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/resolv/tst-resolv-txnid-collision.c b/resolv/tst-resolv-txnid-collision.c
index 611d37362f..189b76f126 100644
--- a/resolv/tst-resolv-txnid-collision.c
+++ b/resolv/tst-resolv-txnid-collision.c
@@ -309,6 +309,11 @@ do_test (void)
     ((struct resolv_redirect_config)
      {
        .response_callback = response,
+
+       /* The response callback use global state (the previous_*
+          variables), and query processing must therefore be
+          serialized.  */
+       .single_thread_udp = true,
      });
 
   for (int rcode = 0; rcode <= 5; ++rcode)

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