Re: [PATCH 1/3] rcu: Use static initializer for krc.lock

[Uladzislau Rezki <urezki@gmail.com>]

On Thu, Apr 16, 2020 at 12:53:27PM -0700, Paul E. McKenney wrote:
> 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@joelfernandes.org> 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?
> 
Paul, just to make it more clear, even invoking two arguments fkree_rcu()
currently does an allocation. We maintain an array that contains pointers
for "bulk logic". 

--
Vlad Rezki