CVE-2026-80866

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

tipc: avoid busy looping in tipc exit net()

Blamed commit introduced a busy-wait loop in tipc exit net() to wait for pending UDP bearer cleanup works to complete:

while (atomic read(&tn->wq count))
    cond resched();

This loop can busy-wait for a long time if cond resched() is a NOP. This typically happens if the netns exit is executed by a high priority task, or under kernels configured without preemption (CONFIG PREEMPT NONE). In such cases, it wastes CPU cycles and can lead to soft lockups.

Fix this by replacing the busy loop with wait var event(), allowing the thread to sleep properly until the work queue count reaches zero.

Accordingly, update cleanup bearer() to use atomic dec and test() and wake up var() to wake up the waiter when the count drops to zero.

This uses the global wait queue hash table, avoiding the need to bloat struct tipc net with a wait queue head t. The atomic dec and test() provides the necessary memory barrier to ensure the wakeup is not missed.