CVE-2024-42245

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> Revert "sched/fair: Make sure to try to detach at least one movable task"<br /> <br /> This reverts commit b0defa7ae03ecf91b8bfd10ede430cff12fcbd06.<br /> <br /> b0defa7ae03ec changed the load balancing logic to ignore env.max_loop if<br /> all tasks examined to that point were pinned. The goal of the patch was<br /> to make it more likely to be able to detach a task buried in a long list<br /> of pinned tasks. However, this has the unfortunate side effect of<br /> creating an O(n) iteration in detach_tasks(), as we now must fully<br /> iterate every task on a cpu if all or most are pinned. Since this load<br /> balance code is done with rq lock held, and often in softirq context, it<br /> is very easy to trigger hard lockups. We observed such hard lockups with<br /> a user who affined O(10k) threads to a single cpu.<br /> <br /> When I discussed this with Vincent he initially suggested that we keep<br /> the limit on the number of tasks to detach, but increase the number of<br /> tasks we can search. However, after some back and forth on the mailing<br /> list, he recommended we instead revert the original patch, as it seems<br /> likely no one was actually getting hit by the original issue.