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SubjectRe: [rcu:dev.2019.09.23a 62/77] kernel/rcu/tree.c:2882 kfree_call_rcu() warn: inconsistent returns 'irqsave:flags'.
On Tue, Sep 24, 2019 at 09:03:48AM -0700, Paul E. McKenney wrote:
> On Tue, Sep 24, 2019 at 08:15:12AM -0400, Joel Fernandes wrote:
> > On Tue, Sep 24, 2019 at 4:05 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > >
> > > tree: https://kernel.googlesource.com/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2019.09.23a
> > > head: 97de53b94582c208ee239178b208b8e8b9472585
> > > commit: 39676bb72323718a9e7bab1ba9c4a68319a96f62 [62/77] rcu: Add support for debug_objects debugging for kfree_rcu()
> > >
> > > If you fix the issue, kindly add following tag
> > > Reported-by: kbuild test robot <lkp@intel.com>
> > > Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> > >
> > > smatch warnings:
> > > kernel/rcu/tree.c:2882 kfree_call_rcu() warn: inconsistent returns 'irqsave:flags'.
> > > Locked on: line 2867
> > > Unlocked on: line 2882
> > >
> > > git remote add rcu https://kernel.googlesource.com/pub/scm/linux/kernel/git/paulmck/linux-rcu.git
> > > git remote update rcu
> > > git checkout 39676bb72323718a9e7bab1ba9c4a68319a96f62
> > > vim +2882 kernel/rcu/tree.c
> > >
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2850) void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2851) {
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2852) unsigned long flags;
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2853) struct kfree_rcu_cpu *krcp;
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2854)
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2855) head->func = func;
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2856)
> > > 87970ccf5a9125 Paul E. McKenney 2019-09-19 2857 local_irq_save(flags); // For safely calling this_cpu_ptr().
> > > ^^^^^^^^^^^^^^^^^^^^^
> > > IRQs disabled.
> > >
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2858) krcp = this_cpu_ptr(&krc);
> > > ff8db005e371cb Paul E. McKenney 2019-09-19 2859 if (krcp->initialized)
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2860) spin_lock(&krcp->lock);
> > > 5f5046cc15d514 Joel Fernandes (Google 2019-08-05 2861)
> > > 87970ccf5a9125 Paul E. McKenney 2019-09-19 2862 // Queue the object but don't yet schedule the batch.
> > > 39676bb7232371 Joel Fernandes (Google 2019-09-22 2863) if (debug_rcu_head_queue(head)) {
> > > 39676bb7232371 Joel Fernandes (Google 2019-09-22 2864) // Probable double kfree_rcu(), just leak.
> > > 39676bb7232371 Joel Fernandes (Google 2019-09-22 2865) WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
> > > 39676bb7232371 Joel Fernandes (Google 2019-09-22 2866) __func__, head);
> > > 39676bb7232371 Joel Fernandes (Google 2019-09-22 2867) return;
> > >
> > > Need to re-enable before returning.
> >
> > Right. At this point the system has a bug anyway since it is a
> > double-free. But yes, no reason to introduce more bugs. Will fix.
> > Thank you, Dan!
>
> What Joel said!
>
> As long as I am doing several other reports anyway...
>
> How does the to-be-squashed patch below look?

Hi Paul,

Sorry for the late reply due to the conference..

This patch looks Ok, the code in your tree though is slightly different mine
I think because you reworked the kfree_rcu() code for working during early
boot.

After my talk tomorrow, I will go through your rcu/dev tree in detail to
review the reworks you did in detail.

Let me know if you have the kfree_rcu() changes in a separate topic branch,
as well. So it will make reviewing easier.

thanks,

- Joel


>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit 39af4c08038a8a6a7b1c9804fdd2c1921d583222
> Author: Paul E. McKenney <paulmck@kernel.org>
> Date: Tue Sep 24 09:02:00 2019 -0700
>
> squash! rcu: Add support for debug_objects debugging for kfree_rcu()
>
> [ paulmck: Fix IRQ per kbuild test robot <lkp@intel.com> feedback. ]
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 921daa7..edb7539 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2870,7 +2870,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> // Probable double kfree_rcu(), just leak.
> WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
> __func__, head);
> - return;
> + goto unlock_return;
> }
> head->func = func;
> head->next = krcp->head;
> @@ -2883,6 +2883,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
> schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
> }
>
> +unlock_return:
> if (krcp->initialized)
> spin_unlock(&krcp->lock);
> local_irq_restore(flags);

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