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Date:   Fri, 23 Dec 2016 03:55:30 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     kbuild-all@...org, mingo@...nel.org, peterz@...radead.org,
        oleg@...hat.com, linux-kernel@...r.kernel.org, dave@...olabs.net,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 1/2] sched: Introduce rcuwait machinery

Hi Davidlohr,

[auto build test ERROR on tip/auto-latest]
[also build test ERROR on v4.9 next-20161222]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Davidlohr-Bueso/sched-Introduce-rcuwait/20161223-020109
config: m68k-sun3_defconfig (attached as .config)
compiler: m68k-linux-gcc (GCC) 4.9.0
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=m68k 

Note: the linux-review/Davidlohr-Bueso/sched-Introduce-rcuwait/20161223-020109 HEAD 9e9d238f94d5aa8e348e7e70585533fe0dbd373b builds fine.
      It only hurts bisectibility.

All error/warnings (new ones prefixed by >>):

>> kernel/exit.c:285:29: warning: 'struct rcuwait' declared inside parameter list
    void rcuwait_trywake(struct rcuwait *w)
                                ^
>> kernel/exit.c:285:29: warning: its scope is only this definition or declaration, which is probably not what you want
   In file included from include/linux/srcu.h:33:0,
                    from include/linux/notifier.h:15,
                    from include/linux/memory_hotplug.h:6,
                    from include/linux/mmzone.h:751,
                    from include/linux/gfp.h:5,
                    from include/linux/mm.h:9,
                    from kernel/exit.c:7:
   kernel/exit.c: In function 'rcuwait_trywake':
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/rcupdate.h:606:10: note: in definition of macro '__rcu_dereference_check'
     typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
             ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/rcupdate.h:606:36: note: in definition of macro '__rcu_dereference_check'
     typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
                                       ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
   In file included from include/asm-generic/bug.h:4:0,
                    from arch/m68k/include/asm/bug.h:28,
                    from include/linux/bug.h:4,
                    from include/linux/mmdebug.h:4,
                    from include/linux/mm.h:8,
                    from kernel/exit.c:7:
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/compiler.h:563:9: note: in definition of macro 'lockless_dereference'
     typeof(p) _________p1 = READ_ONCE(p); \
            ^
   include/linux/rcupdate.h:727:2: note: in expansion of macro '__rcu_dereference_check'
     __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
     ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
   In file included from include/asm-generic/bug.h:4:0,
                    from arch/m68k/include/asm/bug.h:28,
                    from include/linux/bug.h:4,
                    from include/linux/mmdebug.h:4,
                    from include/linux/mm.h:8,
                    from kernel/exit.c:7:
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/compiler.h:305:17: note: in definition of macro '__READ_ONCE'
     union { typeof(x) __val; char __c[1]; } __u;   \
                    ^
>> include/linux/compiler.h:563:26: note: in expansion of macro 'READ_ONCE'
     typeof(p) _________p1 = READ_ONCE(p); \
                             ^
>> include/linux/rcupdate.h:606:48: note: in expansion of macro 'lockless_dereference'
     typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
                                                   ^
   include/linux/rcupdate.h:727:2: note: in expansion of macro '__rcu_dereference_check'
     __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
     ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/compiler.h:307:22: note: in definition of macro '__READ_ONCE'
      __read_once_size(&(x), __u.__c, sizeof(x));  \
                         ^
>> include/linux/compiler.h:563:26: note: in expansion of macro 'READ_ONCE'
     typeof(p) _________p1 = READ_ONCE(p); \
                             ^
>> include/linux/rcupdate.h:606:48: note: in expansion of macro 'lockless_dereference'
     typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
                                                   ^
   include/linux/rcupdate.h:727:2: note: in expansion of macro '__rcu_dereference_check'
     __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
     ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/compiler.h:307:42: note: in definition of macro '__READ_ONCE'
      __read_once_size(&(x), __u.__c, sizeof(x));  \
                                             ^
>> include/linux/compiler.h:563:26: note: in expansion of macro 'READ_ONCE'
     typeof(p) _________p1 = READ_ONCE(p); \
                             ^
>> include/linux/rcupdate.h:606:48: note: in expansion of macro 'lockless_dereference'
     typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
                                                   ^
   include/linux/rcupdate.h:727:2: note: in expansion of macro '__rcu_dereference_check'
     __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
     ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/compiler.h:309:30: note: in definition of macro '__READ_ONCE'
      __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
                                 ^
>> include/linux/compiler.h:563:26: note: in expansion of macro 'READ_ONCE'
     typeof(p) _________p1 = READ_ONCE(p); \
                             ^
>> include/linux/rcupdate.h:606:48: note: in expansion of macro 'lockless_dereference'
     typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
                                                   ^
   include/linux/rcupdate.h:727:2: note: in expansion of macro '__rcu_dereference_check'
     __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
     ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
>> kernel/exit.c:308:26: error: dereferencing pointer to incomplete type
     task = rcu_dereference(w->task);
                             ^
   include/linux/compiler.h:309:50: note: in definition of macro '__READ_ONCE'
      __read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \
                                                     ^
>> include/linux/compiler.h:563:26: note: in expansion of macro 'READ_ONCE'
     typeof(p) _________p1 = READ_ONCE(p); \
                             ^
>> include/linux/rcupdate.h:606:48: note: in expansion of macro 'lockless_dereference'
     typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
                                                   ^
   include/linux/rcupdate.h:727:2: note: in expansion of macro '__rcu_dereference_check'
     __rcu_dereference_check((p), (c) || rcu_read_lock_held(), __rcu)
     ^
   include/linux/rcupdate.h:786:28: note: in expansion of macro 'rcu_dereference_check'
    #define rcu_dereference(p) rcu_dereference_check(p, 0)
                               ^
   kernel/exit.c:308:9: note: in expansion of macro 'rcu_dereference'
     task = rcu_dereference(w->task);
            ^
   In file included from include/asm-generic/bug.h:4:0,
                    from arch/m68k/include/asm/bug.h:28,
                    from include/linux/bug.h:4,
                    from include/linux/mmdebug.h:4,
                    from include/linux/mm.h:8,
                    from kernel/exit.c:7:

vim +308 kernel/exit.c

   279		if (!sighand)
   280			return NULL;
   281	
   282		return task;
   283	}
   284	
 > 285	void rcuwait_trywake(struct rcuwait *w)
   286	{
   287		struct task_struct *task;
   288	
   289		rcu_read_lock();
   290	
   291		/*
   292		 * Order condition vs @task, such that everything prior to the load
   293		 * of @task is visible. This is the condition as to why the user called
   294		 * rcuwait_trywake() in the first place. Pairs with set_current_state()
   295		 * barrier (A) in rcuwait_wait_event().
   296		 *
   297		 *    WAIT                WAKE
   298		 *    [S] tsk = current	  [S] cond = true
   299		 *        MB (A)	      MB (B)
   300		 *    [L] cond		  [L] tsk
   301		 */
   302		smp_rmb(); /* (B) */
   303	
   304		/*
   305		 * Avoid using task_rcu_dereference() magic as long as we are careful,
   306		 * see comment in rcuwait_wait_event() regarding ->exit_state.
   307		 */
 > 308		task = rcu_dereference(w->task);
   309		if (task)
   310			wake_up_process(task);
   311		rcu_read_unlock();

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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