On 2023-06-15 09:43:11 [-0700], Paul E. McKenney wrote: > On Wed, Jun 14, 2023 at 10:34:30AM +0200, Sebastian Andrzej Siewior wrote: > > bpf_free_inode() is invoked as a RCU callback. Usually RCU callbacks are > > invoked within softirq context. By setting rcutree.use_softirq=0 boot > > option the RCU callbacks will be invoked in a per-CPU kthread with > > bottom halves disabled which implies a RCU read section. > > > > On PREEMPT_RT the context remains fully preemptible. The RCU read > > section however does not allow schedule() invocation. The latter happens > > in mutex_lock() performed by bpf_trampoline_unlink_prog() originated > > from bpf_link_put(). > > Just to make sure that I understand, you are proposing that the RCU > callbacks continue to run with BH disabled, but that BH-disabled regions > are preemptible in kernels built with CONFIG_PREEMPT_RT=y? > > Or did I miss a turn in there somewhere? I'm not proposing anything, just stating what we have. On PREEMPT_RT you are preemptible within the RCU callback but must not invoke schedule(). Similar to the RCU read section on CONFIG_PREEMPT where you are preemptible but must not invoke schedule(). > > Thanx, Paul Sebastian
