Re: [RT BUG] Stall caused by eventpoll, rwlocks and CFS bandwidth controller

[Sebastian Andrzej Siewior]

On 2025-04-14 20:20:04 [+0530], K Prateek Nayak wrote:
> Note: I could not reproduce the splat with !PREEMPT_RT kernel
> (CONFIG_PREEMPT=y) or with small loops counts that don't exhaust the
> cfs bandwidth.

Not sure what this has to do with anything.
On !RT the read_lock() in the timer can be acquired even with a pending
writer. The writer keeps spinning until the main thread is gone. There
should be no RCU boosting but the RCU still is there, too.

On RT the read_lock() in the timer block, the write blocks, too. So
every blocker on the lock is scheduled out until the reader is gone. On
top of that, the reader gets RCU boosted with FIFO-1 by default to get
out.

Sebastian