2019-08-27 19:03:33

by Joel Fernandes

Subject: [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()

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) <[email protected]>
---
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

2019-08-28 21:34:22

by Paul E. McKenney

Subject: Re: [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()

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) <[email protected]>

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
>

2019-08-28 21:45:30

by Joel Fernandes

Subject: Re: [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()

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) <[email protected]>
>
> 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
> >

2019-08-28 21:59:32

by Paul E. McKenney

Subject: Re: [PATCH 3/5] rcu/tree: Add support for debug_objects debugging for kfree_rcu()

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) <[email protected]>
> >
> > 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
> > >