CVE-2025-38393

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

NFSv4/pNFS: Fix a race to wake on NFSLAYOUTDRAIN

We found a few different systems hung up in writeback waiting on the same page lock, and one task waiting on the NFSLAYOUTDRAIN bit in pnfsupdatelayout(), however the pnfslayouthdr's plh_outstanding count was zero.

It seems most likely that this is another race between the waiter and waker similar to commit ed0172af5d6f ("SUNRPC: Fix a race to wake a sync task"). Fix it up by applying the advised barrier.