CVE-2026-72437: md/raid1: free r1_bio when REQ_NOWAIT is set and read would block on retry

In the Linux kernel, the following vulnerability has been resolved:

md/raid1: free r1bio when REQNOWAIT is set and read would block on retry

When a read is retried, raid1readrequest() may be called with a pre-allocated r1bio. If waitreadbarrier() fails for a REQNOWAIT read, the bio is completed and the function returns immediately. In this case the existing r1bio is leaked.

This fixes a leak of pre-allocated r1bio structures for retried reads.