md/raid1: fix writes_pending and barrier reference leaks on write failures

In the Linux kernel, the following vulnerability has been resolved: md/raid1: fix writes_pending and barrier reference leaks on write failures raid1_make_request() acquires a writes_pending reference with md_write_start() before calling raid1_write_request(). Several failure paths in raid1_write_request() complete the bio and return without reaching the normal write completion path, causing the corresponding md_write_end() to be skipped. Make raid1_write_request() return a status indicating whether the write request was successfully queued. This allows raid1_make_request() to call md_write_end() when raid1_write_request() fails. Additionally, if wait_blocked_rdev() fails after wait_barrier() succeeds, the associated barrier reference is not released. Call allow_barrier() before returning from that path to keep the barrier accounting balanced.

Where it's fixed