1.6 KiB
CVE-2024-42245
Description
In the Linux kernel, the following vulnerability has been resolved:Revert "sched/fair: Make sure to try to detach at least one movable task"This reverts commit b0defa7ae03ecf91b8bfd10ede430cff12fcbd06.b0defa7ae03ec changed the load balancing logic to ignore env.max_loop ifall tasks examined to that point were pinned. The goal of the patch wasto make it more likely to be able to detach a task buried in a long listof pinned tasks. However, this has the unfortunate side effect ofcreating an O(n) iteration in detach_tasks(), as we now must fullyiterate every task on a cpu if all or most are pinned. Since this loadbalance code is done with rq lock held, and often in softirq context, itis very easy to trigger hard lockups. We observed such hard lockups witha user who affined O(10k) threads to a single cpu.When I discussed this with Vincent he initially suggested that we keepthe limit on the number of tasks to detach, but increase the number oftasks we can search. However, after some back and forth on the mailinglist, he recommended we instead revert the original patch, as it seemslikely no one was actually getting hit by the original issue.
POC
Reference
No PoCs from references.