Messages in this thread | | | Date | Wed, 23 Feb 2011 08:59:01 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH RFC tip/core/rcu 05/11] rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT. |
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* Steven Rostedt (rostedt@goodmis.org) wrote: > On Tue, 2011-02-22 at 17:39 -0800, Paul E. McKenney wrote: > > The build will break if you change the Kconfig to allow > > DEBUG_OBJECTS_RCU_HEAD and !PREEMPT, so document the reasoning > > near where the breakage would occur. > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > --- > > kernel/rcupdate.c | 5 +++++ > > 1 files changed, 5 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c > > index afd21d1..f3240e9 100644 > > --- a/kernel/rcupdate.c > > +++ b/kernel/rcupdate.c > > @@ -214,6 +214,11 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) > > * Ensure that queued callbacks are all executed. > > * If we detect that we are nested in a RCU read-side critical > > * section, we should simply fail, otherwise we would deadlock. > > + * Note that the machinery to reliably determine whether > > + * or not we are in an RCU read-side critical section > > + * exists only in the preemptible RCU implementations > > + * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why > > + * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT. > > */ > > Shouldn't this comment also be in the kconfig where > DEBUG_OBJECTS_RCU_HEAD is defined?
hrm, but this is a "rcuhead_fixup_init" : it does not need to always succeed. It's just that when it is safe to recover from an error situation, it does it. We could do:
#ifdef CONFIG_PREEMPT /* * Ensure that queued callbacks are all executed. * If we detect that we are nested in a RCU read-side * critical * section, we should simply fail, otherwise we would * deadlock. */ if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { WARN_ON(1); return 0; } rcu_barrier(); rcu_barrier_sched(); rcu_barrier_bh(); debug_object_init(head, &rcuhead_debug_descr); return 1; #else return 0; #endif
instead, no ?
Mathieu
> > -- Steve > > > if (rcu_preempt_depth() != 0 || preempt_count() != 0 || > > irqs_disabled()) { > >
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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