linux-kernel - Re: [rcu:dev.2019.04.16a 38/72] kernel/rcu/tree.c:2408:36: sparse: sparse: incorrect type in initializer (different address spaces)

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Date:   Tue, 23 Apr 2019 17:08:14 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     kbuild test robot <lkp@...el.com>, kbuild-all@...org,
        linux-kernel@...r.kernel.org
Subject: Re: [rcu:dev.2019.04.16a 38/72] kernel/rcu/tree.c:2408:36: sparse:
 sparse: incorrect type in initializer (different address spaces)

On 2019-04-23 05:46:19 [-0700], Paul E. McKenney wrote:
> On Tue, Apr 23, 2019 at 06:33:33PM +0800, kbuild test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2019.04.16a
> > head:   ca8714f549be5a186d086a223184095759eb7094
> > commit: 9a1a31194644dfc6b8f19755ea44ecf84f37cf40 [38/72] rcu: Enable elimination of Tree-RCU softirq processing
> > reproduce:
> >         # apt-get install sparse
> >         git checkout 9a1a31194644dfc6b8f19755ea44ecf84f37cf40
> >         make ARCH=x86_64 allmodconfig
> >         make C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__'
> > 
> > If you fix the issue, kindly add following tag
> > Reported-by: kbuild test robot <lkp@...el.com>
> > 
> > 
> > 
> > sparse warnings: (new ones prefixed by >>)
> > 
> > >> kernel/rcu/tree.c:2408:36: sparse: sparse: incorrect type in initializer (different address spaces) @@    expected struct task_struct [noderef] <asn:3> **store @@    got struct task_struct [noderef] <asn:3> **store @@
> 
> Line 2408 of kernel/rcu/tree.c for commit 9a1a31194644 ("rcu: Enable
> elimination of Tree-RCU softirq processing") is this:
> 
> 	.store			= &rcu_data.rcu_cpu_kthread_task,
> 
> So I am having some difficulty understanding this sparse diagnostic.
> 
> Help?

this helps

diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
index d0884b5250010..c2678e29807c1 100644
--- a/include/linux/smpboot.h
+++ b/include/linux/smpboot.h
@@ -29,7 +29,7 @@ struct smpboot_thread_data;
  * @thread_comm:	The base name of the thread
  */
 struct smp_hotplug_thread {
-	struct task_struct __percpu	**store;
+	struct task_struct		*__percpu *store;
 	struct list_head		list;
 	int				(*thread_should_run)(unsigned int cpu);
 	void				(*thread_fn)(unsigned int cpu);


I just need to find the correct words for it.
And yes, it is not RCU related…

> 							Thanx, Paul

Sebastian