selftests/namespaces: Fix racy pipe handshake in timens and pidns_separate

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In timens_separate and pidns_separate both the child and the grandchild
write a 'Y' readiness byte to the same pipe, but the parent expects a
single 'Y' followed by the grandchild's pid. If the grandchild's byte
arrives first, the parent takes it for the child's and reads the pid
misaligned, ending up with a garbage value.

The parent stores that pid in self->grandchild_pid so that
FIXTURE_TEARDOWN() can kill the grandchild. A garbage pid leaves the real
grandchild alive in pause(), holding the test runner's TAP pipe open and
hanging the whole collection.

The grandchild has nothing to report, so drop its write() and leave the
child as the sole writer.

Fixes: fdb48976b6 ("selftests/namespaces: Kill grandchild in nsid fixture teardown")
Signed-off-by: Ricardo B. Marlière (SUSE) <ricardo@marliere.net>
Link: https://patch.msgid.link/20260810-selftests-namespaces_race-v1-1-4307e833783e@marliere.net
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

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Ricardo B. Marlière (SUSE) 2026-08-10 17:56:00 -03:00 • committed by Christian Brauner

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tools/testing/selftests/namespaces/nsid_test.c

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