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* [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()
@ 2019-08-27 19:01 Joel Fernandes (Google)
  2019-08-28 21:31 ` Paul E. McKenney
  0 siblings, 1 reply; 4+ messages in thread
From: Joel Fernandes (Google) @ 2019-08-27 19:01 UTC (permalink / raw)
  To: linux-kernel
  Cc: Joel Fernandes (Google),
	byungchul.park, Josh Triplett, Lai Jiangshan, linux-doc,
	Mathieu Desnoyers, Paul E. McKenney, rcu, Steven Rostedt,
	kernel-team

Make use of RCU's debug_objects debugging support
(CONFIG_DEBUG_OBJECTS_RCU_HEAD) similar to call_rcu() and other flavors.
We queue the object during the kfree_rcu() call and dequeue it during
reclaim.

Tested that enabling CONFIG_DEBUG_OBJECTS_RCU_HEAD successfully detects
double kfree_rcu() calls.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/rcu/tree.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 9b9ae4db1c2d..64568f12641d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2757,6 +2757,7 @@ static void kfree_rcu_work(struct work_struct *work)
 	for (; head; head = next) {
 		next = head->next;
 		/* Could be possible to optimize with kfree_bulk in future */
+		debug_rcu_head_unqueue(head);
 		__rcu_reclaim(rcu_state.name, head);
 		cond_resched_tasks_rcu_qs();
 	}
@@ -2868,6 +2869,13 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 	if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING)
 		return kfree_call_rcu_nobatch(head, func);
 
+	if (debug_rcu_head_queue(head)) {
+		/* Probable double kfree_rcu() */
+		WARN_ONCE(1, "kfree_call_rcu(): Double-freed call. rcu_head %p\n",
+			  head);
+		return;
+	}
+
 	head->func = func;
 
 	local_irq_save(flags);	/* For safely calling this_cpu_ptr(). */
-- 
2.23.0.187.g17f5b7556c-goog


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()
  2019-08-27 19:01 [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu() Joel Fernandes (Google)
@ 2019-08-28 21:31 ` Paul E. McKenney
  2019-08-28 21:43   ` Joel Fernandes
  0 siblings, 1 reply; 4+ messages in thread
From: Paul E. McKenney @ 2019-08-28 21:31 UTC (permalink / raw)
  To: Joel Fernandes (Google)
  Cc: linux-kernel, byungchul.park, Josh Triplett, Lai Jiangshan,
	linux-doc, Mathieu Desnoyers, rcu, Steven Rostedt, kernel-team

On Tue, Aug 27, 2019 at 03:01:57PM -0400, Joel Fernandes (Google) wrote:
> Make use of RCU's debug_objects debugging support
> (CONFIG_DEBUG_OBJECTS_RCU_HEAD) similar to call_rcu() and other flavors.

Other flavors?  Ah, call_srcu(), rcu_barrier(), and srcu_barrier(),
right?

> We queue the object during the kfree_rcu() call and dequeue it during
> reclaim.
> 
> Tested that enabling CONFIG_DEBUG_OBJECTS_RCU_HEAD successfully detects
> double kfree_rcu() calls.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

The code looks good!

							Thanx, Paul

> ---
>  kernel/rcu/tree.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 9b9ae4db1c2d..64568f12641d 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2757,6 +2757,7 @@ static void kfree_rcu_work(struct work_struct *work)
>  	for (; head; head = next) {
>  		next = head->next;
>  		/* Could be possible to optimize with kfree_bulk in future */
> +		debug_rcu_head_unqueue(head);
>  		__rcu_reclaim(rcu_state.name, head);
>  		cond_resched_tasks_rcu_qs();
>  	}
> @@ -2868,6 +2869,13 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
>  	if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING)
>  		return kfree_call_rcu_nobatch(head, func);
>  
> +	if (debug_rcu_head_queue(head)) {
> +		/* Probable double kfree_rcu() */
> +		WARN_ONCE(1, "kfree_call_rcu(): Double-freed call. rcu_head %p\n",
> +			  head);
> +		return;
> +	}
> +
>  	head->func = func;
>  
>  	local_irq_save(flags);	/* For safely calling this_cpu_ptr(). */
> -- 
> 2.23.0.187.g17f5b7556c-goog
> 

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()
  2019-08-28 21:31 ` Paul E. McKenney
@ 2019-08-28 21:43   ` Joel Fernandes
  2019-08-28 21:57     ` Paul E. McKenney
  0 siblings, 1 reply; 4+ messages in thread
From: Joel Fernandes @ 2019-08-28 21:43 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, byungchul.park, Josh Triplett, Lai Jiangshan,
	linux-doc, Mathieu Desnoyers, rcu, Steven Rostedt, kernel-team

On Wed, Aug 28, 2019 at 02:31:19PM -0700, Paul E. McKenney wrote:
> On Tue, Aug 27, 2019 at 03:01:57PM -0400, Joel Fernandes (Google) wrote:
> > Make use of RCU's debug_objects debugging support
> > (CONFIG_DEBUG_OBJECTS_RCU_HEAD) similar to call_rcu() and other flavors.
> 
> Other flavors?  Ah, call_srcu(), rcu_barrier(), and srcu_barrier(),
> right?

Yes.

> > We queue the object during the kfree_rcu() call and dequeue it during
> > reclaim.
> > 
> > Tested that enabling CONFIG_DEBUG_OBJECTS_RCU_HEAD successfully detects
> > double kfree_rcu() calls.
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> The code looks good!

thanks, does that mean you'll ack/apply it? :-P

 - Joel

> 
> 							Thanx, Paul
> 
> > ---
> >  kernel/rcu/tree.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 9b9ae4db1c2d..64568f12641d 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -2757,6 +2757,7 @@ static void kfree_rcu_work(struct work_struct *work)
> >  	for (; head; head = next) {
> >  		next = head->next;
> >  		/* Could be possible to optimize with kfree_bulk in future */
> > +		debug_rcu_head_unqueue(head);
> >  		__rcu_reclaim(rcu_state.name, head);
> >  		cond_resched_tasks_rcu_qs();
> >  	}
> > @@ -2868,6 +2869,13 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> >  	if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING)
> >  		return kfree_call_rcu_nobatch(head, func);
> >  
> > +	if (debug_rcu_head_queue(head)) {
> > +		/* Probable double kfree_rcu() */
> > +		WARN_ONCE(1, "kfree_call_rcu(): Double-freed call. rcu_head %p\n",
> > +			  head);
> > +		return;
> > +	}
> > +
> >  	head->func = func;
> >  
> >  	local_irq_save(flags);	/* For safely calling this_cpu_ptr(). */
> > -- 
> > 2.23.0.187.g17f5b7556c-goog
> > 

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()
  2019-08-28 21:43   ` Joel Fernandes
@ 2019-08-28 21:57     ` Paul E. McKenney
  0 siblings, 0 replies; 4+ messages in thread
From: Paul E. McKenney @ 2019-08-28 21:57 UTC (permalink / raw)
  To: Joel Fernandes
  Cc: linux-kernel, byungchul.park, Josh Triplett, Lai Jiangshan,
	linux-doc, Mathieu Desnoyers, rcu, Steven Rostedt, kernel-team

On Wed, Aug 28, 2019 at 05:43:20PM -0400, Joel Fernandes wrote:
> On Wed, Aug 28, 2019 at 02:31:19PM -0700, Paul E. McKenney wrote:
> > On Tue, Aug 27, 2019 at 03:01:57PM -0400, Joel Fernandes (Google) wrote:
> > > Make use of RCU's debug_objects debugging support
> > > (CONFIG_DEBUG_OBJECTS_RCU_HEAD) similar to call_rcu() and other flavors.
> > 
> > Other flavors?  Ah, call_srcu(), rcu_barrier(), and srcu_barrier(),
> > right?
> 
> Yes.
> 
> > > We queue the object during the kfree_rcu() call and dequeue it during
> > > reclaim.
> > > 
> > > Tested that enabling CONFIG_DEBUG_OBJECTS_RCU_HEAD successfully detects
> > > double kfree_rcu() calls.
> > > 
> > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > 
> > The code looks good!
> 
> thanks, does that mean you'll ack/apply it? :-P

Is it independent of 1/5 and 2/5?

							Thanx, Paul

>  - Joel
> 
> > 
> > 							Thanx, Paul
> > 
> > > ---
> > >  kernel/rcu/tree.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > > 
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 9b9ae4db1c2d..64568f12641d 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -2757,6 +2757,7 @@ static void kfree_rcu_work(struct work_struct *work)
> > >  	for (; head; head = next) {
> > >  		next = head->next;
> > >  		/* Could be possible to optimize with kfree_bulk in future */
> > > +		debug_rcu_head_unqueue(head);
> > >  		__rcu_reclaim(rcu_state.name, head);
> > >  		cond_resched_tasks_rcu_qs();
> > >  	}
> > > @@ -2868,6 +2869,13 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> > >  	if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING)
> > >  		return kfree_call_rcu_nobatch(head, func);
> > >  
> > > +	if (debug_rcu_head_queue(head)) {
> > > +		/* Probable double kfree_rcu() */
> > > +		WARN_ONCE(1, "kfree_call_rcu(): Double-freed call. rcu_head %p\n",
> > > +			  head);
> > > +		return;
> > > +	}
> > > +
> > >  	head->func = func;
> > >  
> > >  	local_irq_save(flags);	/* For safely calling this_cpu_ptr(). */
> > > -- 
> > > 2.23.0.187.g17f5b7556c-goog
> > > 

^ permalink raw reply	[flat|nested] 4+ messages in thread

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2019-08-27 19:01 [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu() Joel Fernandes (Google)
2019-08-28 21:31 ` Paul E. McKenney
2019-08-28 21:43   ` Joel Fernandes
2019-08-28 21:57     ` Paul E. McKenney

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