On Tue, Jul 11, 2023 at 10:52:02AM +0800, Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote: > commit 2bdfd2825c9662463371e6691b1a794e97fa36b4 > Author: Waiman Long <longman@xxxxxxxxxx> > Date: Wed Feb 2 22:31:03 2022 -0500 > > cgroup/cpuset: Fix "suspicious RCU usage" lockdep warning Aha, thanks for the pointer. I've also found a paragraph in [1]: > In addition, the -rt patchset turns spinlocks into a sleeping locks so > that the corresponding critical sections can be preempted, which also > means that these sleeplockified spinlocks (but not other sleeping > locks!) may be acquire within -rt-Linux-kernel RCU read-side critical > sections. That suggests (together with practical use) that dicussed spinlocks should be fine in RCU read section. And the possible reason is deeper in generate_sched_domains() that do kmalloc(..., GFP_KERNEL). Alas update_cpumask_hier() still calls generate_sched_domains(), OTOH, update_parent_subparts_cpumask() doesn't seem so. The idea to not relieve rcu_read_lock() in update_cpumask() iteration (instead of the technically unneeded refcnt bump) would have to be verified with CONFIG_PROVE_RCU && CONFIG_LOCKDEP. WDYT? Michal [1] https://www.kernel.org/doc/html/latest/RCU/Design/Requirements/Requirements.html?highlight=rcu+read+section#specialization
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