linux-kernel - Re: [PATCH] rcu: do not include rtmutex

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Message-Id: <20171018153946.GH3521@linux.vnet.ibm.com>
Date:   Wed, 18 Oct 2017 08:39:46 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     kbuild test robot <fengguang.wu@...el.com>, kbuild-all@...org,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu: do not include rtmutex_common.h unconditionally

On Wed, Oct 18, 2017 at 10:34:36AM +0200, Sebastian Andrzej Siewior wrote:
> Since commit bcda31a26594 ("rcu: Suppress lockdep false-positive
> ->boost_mtx complaints") the rtmutex_common.h is included
> unconditionally. This break CONFIG_FUTEX=n configs which do not have
> CONFIG_RT_MUTEX enabled which leads to the lack of certain members in
> task_struct which are accessed in rtmutex_common.h as reported by the kbuild
> test robot:
> |   In file included from include/uapi/linux/stddef.h:1:0,
> |                    from include/linux/stddef.h:4,
> |                    from include/uapi/linux/posix_types.h:4,
> |                    from include/uapi/linux/types.h:13,
> |                    from include/linux/types.h:5,
> |                    from kernel/rcu/tree.c:30:
> |   kernel/rcu/../locking/rtmutex_common.h: In function 'task_has_pi_waiters':
> |>> kernel/rcu/../locking/rtmutex_common.h:62:26: error: 'struct task_struct' has no member named 'pi_waiters'; did you mean 'cpu_timers'?
> 
> among other things.
> I move the include back to the RCU_BOOST ifdef and add there the
> rt_mutex_futex_unlock define like we already have it for rt_mutex_owner
> for the same reason.
> While at it, I remove the second rtmutex_common.h include within the
> RCU_BOOST block because one of those is enough.
> 
> Fixes: bcda31a26594 ("rcu: Suppress lockdep false-positive ->boost_mtx complaints")
> Reported-by: kbuild test robot <fengguang.wu@...el.com>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Thank you very much, hand-applied as a preparatory patch for
"Suppress lockdep false-positive ->boost_mtx complaints", please see
below.

What I don't understand is why 0day test robot didn't complain about
my copy of the exact same patch.  Or maybe it did and I fat-fingered it?
Except that I have gotten "BUILD SUCCESS" reports for commits including
that one.

Ah well, hopefully all is well that ends well...

> ---
> On 2017-10-18 09:32:09 [+0200], To Paul E. McKenney wrote:
> >  I will
> > look at this once I made some slides…
> 
> slides, who needs those anyway…

Best of everything on the presentation, and hope that I didn't mess
you up too badly.

							Thanx, Paul

------------------------------------------------------------------------

commit a06f537e75ea0a9e81245ede1b97bb3a5762b81b
Author: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Date:   Wed Oct 18 08:33:44 2017 -0700

    rcu: do not include rtmutex_common.h unconditionally
    
    This commit adjusts include files and provides definitions in preparation
    for suppressing lockdep false-positive ->boost_mtx complaints.  Without
    this preparation, architectures not supporting rt_mutex will get build
    failures.
    
    Reported-by: kbuild test robot <fengguang.wu@...el.com>
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index fed95fa941e6..969eae45f05d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -54,6 +54,7 @@ DEFINE_PER_CPU(char, rcu_cpu_has_work);
  * This probably needs to be excluded from -rt builds.
  */
 #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
+#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
 
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
@@ -911,8 +912,6 @@ void exit_rcu(void)
 
 #ifdef CONFIG_RCU_BOOST
 
-#include "../locking/rtmutex_common.h"
-
 static void rcu_wake_cond(struct task_struct *t, int status)
 {
 	/*