On Thu, Apr 16, 2020 at 03:26:23PM -0400, Steven Rostedt wrote: > On Thu, 16 Apr 2020 14:59:34 -0400 > Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: > > > But, then will it be safe for kfree_rcu() callers from hard IRQ context to > > call this in PREEMPT_RT? That could would just break then as you cannot sleep > > in hard IRQ context even on PREEMPT_RT. > > But where in PREEMPT_RT would it be called in hard IRQ context? I believe that call_rcu() is invoked with raw spinlocks held, so we should allow kfree_rcu() to be invoked from similar contexts. It obviously cannot allocate memory in such contexts, so perhaps the rule is that single-argument kfree_rcu() cannot be invoked within hard IRQ contexts or with raw spinlocks held. In those contexts, you would instead need to invoke two-argument kfree_rcu(), which never needs to allocate memory. Seem reasonable? Thanx, Paul > Note, most interrupt handlers in PREEMPT_RT are turned into threads (except > for a very few, which shouldn't be calling kfree_rcu()). > > -- Steve
