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

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Message-ID: <20171018161621.3o7fljv4wl3geutv@linutronix.de>
Date:   Wed, 18 Oct 2017 18:16:21 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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 2017-10-18 08:39:46 [-0700], Paul E. McKenney wrote:
> Thank you very much, hand-applied as a preparatory patch for
> "Suppress lockdep false-positive ->boost_mtx complaints", please see
> below.
okay.

> 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.

I don't know. It is a "defconfig" for m32r. Unless it skipped that one,
dunno.

> 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)
>  {
>  	/*

So this probably works. This is
  https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=rcu%2Fdev&id=a06f537e75ea0a9e81245ede1b97bb3a5762b81b&context=40&ignorews=0&dt=0

and the rtmutex_common is still in the ifdef which confused me at first.
But then you wrote "preparatory" and I saw the following patch
  https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=rcu/next&id=33d7471ce21202ce954993552c2e0298d9e0f031

where you move that include rtmutex_common.h. You shouldn't do that
because "rt_mutex_futex_unlock()" has been added added here for the
!BOOST + TREE case. So I thing this should break your build if you
disable CONFIG_FUTEX (which in turn unselects CONFIg_RT_MUTEX).

Sebastian