Re: [RFC][PATCH] sched/ext: Avoid null ptr traversal when ->put_prev_task() is called with NULL next

[Kuba Piecuch]

On Mon Dec 8, 2025 at 10:10 AM UTC, Kuba Piecuch wrote:
> It looks like it's impossible for an outside observer holding a CPU's rq lock
> to observe a task that is running on that CPU and isn't queued, i.e.
> 'running' implies 'queued' (I'm new to the scheduler so I may be wrong here).

A task that blocks in __schedule() can drop the rq lock while picking the next
task, which is after try_to_block_task() dequeues prev. So it's very much
possible for a task on another CPU to grab the rq lock and observe prev as
dequeued but still running.