CVE-2025-21631 block, bfq: fix waker_bfqq UAF after bfq_split_bfqq()

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Multiple CVEs Address UAF Vulnerabilities in BFQ Implementation Three CVEs have been published addressing use-after-free (UAF) vulnerabilities in the BFQ (Budget Fair Queueing) implementation. CVE-2024-49854 and CVE-2024-47706 were published on October 21, 2024, while CVE-2025-21631 was published on January 19, 2025. These vulnerabilities could potentially affect systems utilizing the BFQ scheduler. 4 sources 39