Re: [PATCH] net: raise RCU qs after each threaded NAPI poll
From: Yan Zhai <hidden>
Date: 2024-02-28 16:38:03
Also in:
bpf, lkml, rcu
On Wed, Feb 28, 2024 at 9:37 AM Joel Fernandes [off-list ref] wrote:
Also optionally, I wonder if calling rcu_tasks_qs() directly is better (for documentation if anything) since the issue is Tasks RCU specific. Also code comment above the rcu_softirq_qs() call about cond_resched() not taking care of Tasks RCU would be great!
Yes it's quite surprising to me that cond_resched does not help here,
I will include that comment. Raising just the task RCU QS seems
sufficient to the problem we encountered. But according to commit
d28139c4e967 ("rcu: Apply RCU-bh QSes to RCU-sched and RCU-preempt
when safe"), there might be additional threat factor in __do_softirq
that also applies to threaded poll.
Yan
quoted hunk ↗ jump to hunk
Reviewed-by: Joel Fernandes (Google) <redacted> thanks, - Joel [1]@@ -381,8 +553,10 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) pending >>= softirq_bit; } - if (__this_cpu_read(ksoftirqd) == current) + if (!IS_ENABLED(CONFIG_PREEMPT_RT) && + __this_cpu_read(ksoftirqd) == current) rcu_softirq_qs(); + local_irq_disable();