Merge branch 'bpf: Follow up to RCU enforcement in the verifier.'

Alexei Starovoitov says:

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From: Alexei Starovoitov <ast@kernel.org>

The patch set is addressing a fallout from
commit 6fcd486b

 ("bpf: Refactor RCU enforcement in the verifier.")
It was too aggressive with PTR_UNTRUSTED marks.
Patches 1-6 are cleanup and adding verifier smartness to address real
use cases in bpf programs that broke with too aggressive PTR_UNTRUSTED.
The partial revert is done in patch 7 anyway.
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Signed-off-by: Andrii Nakryiko <andrii@kernel.org>