UBUNTU-CVE-2026-99263: Medium severity ubuntu/linux vulnerability

In the Linux kernel, the following vulnerability has been resolved: iouring/poll: avoid retry wakeup loss when dropping ownership If a wakeup sets IOPOLLRETRYFLAG between the owning task consuming the existing instance of IOPOLLRETRYFLAG and the loop check of iopollcheckevents(), then we stall on processing the request until an unrelated wakeup comes along. Using atomiccmpxchg instead of atomicsubreturn to guarantee both the count v and pollrefs are 0 and no wake-ups are missed.