linux-kernel - Re: [rcu:dev.2019.09.23a 62/77] kernel/rcu/tree.c:2882 kfree_call_rcu() warn: inconsistent returns 'irqsave:flags'.

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Date:   Tue, 24 Sep 2019 08:15:12 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     kbuild@...org, kbuild-all@...org,
        LKML <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: Re: [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 4:05 AM Dan Carpenter <dan.carpenter@...cle.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@...el.com>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.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!