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Date:   Mon, 26 Jul 2021 09:54:21 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Zhouyi Zhou <zhouzhouyi@gmail.com>
Cc:     josh@joshtriplett.org, rostedt@goodmis.org,
        mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
        joel@joelfernandes.org, corbet@lwn.net, ysato@users.sourceforge.jp,
        dalias@libc.org, chris@zankel.net, jcmvbkbc@gmail.com,
        dave@stgolabs.net, tiwai@suse.de, frederic@kernel.org,
        mchehab+huawei@kernel.org, nfraprado@protonmail.com,
        wcohen@redhat.com, tglx@linutronix.de, viro@zeniv.linux.org.uk,
        rric@kernel.org, viresh.kumar@linaro.org, rcu@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org
Subject: Re: [PATCH] RCU: Fix undefined Kconfig macros
Message-ID: <20210726165421.GS4397@paulmck-ThinkPad-P17-Gen-1>
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References: <20210725214333.10623-1-zhouzhouyi@gmail.com>
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On Mon, Jul 26, 2021 at 05:43:33AM +0800, Zhouyi Zhou wrote:
> Hi Paul,
> 
> After I invoking scripts/checkkconfigsymbols.py in linux kernel source
> tree, I find 4 undefined Kconfig macros. I examine them one by one, and
> fix them following your advice.
> 
> 1. TREE_PREEMPT_RCU
> Referencing files: arch/sh/configs/sdk7786_defconfig
> 
> It should now be CONFIG_PREEMPT_RCU. Except that the CONFIG_PREEMPT=y in
> that same file implies CONFIG_PREEMPT_RCU=y, so I delete the
> CONFIG_TREE_PREEMPT_RCU=y line.
> 
> The reason is as follows.
> In kernel/rcu/Kconfig, we have
> config PREEMPT_RCU
>         bool
>         default y if PREEMPTION
> https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt says,
> "The default value is only assigned to the config symbol if no other value
>  was set by the user (via the input prompt above)."
> there is no prompt in config PREEMPT_RCU entry, so we are guaranteed to
> get CONFIG_PREEMPT_RCU=y when CONFIG_PREEMPT is present.
> 
> 2. RCU_CPU_STALL_INFO
> Referencing files: arch/xtensa/configs/nommu_kc705_defconfig
> 
> We now get RCU_CPU_STALL_INFO whether we want it or not, so this
> line should be deleted.
> (RCU_CPU_STALL_INFO is removed in 75c27f119b6475d95374bdad872c6938b5c26196)
> 
> 3. RCU_NOCB_CPU_ALL
> Referencing files:
> Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
> 
> This is an old snapshot of the code. I update this from the real
> rcu_prepare_for_idle() function in kernel/rcu/tree_plugin.h.
> I have invoked "make htmldocs" to ensure the result of above updating.
> 
> 4. RCU_TORTURE_TESTS
> Referencing files: kernel/rcu/rcutorture.c
> 
> forward-progress checking conflicts with CPU-stall testing, so we should
> complain when modprobe the rcutorture.ko if that happens.
> 
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>

Very good, thank you!  I wordsmithed as following and applied for
the v5.16 merge window.

							Thanx, Paul

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

commit 32a4be124ed0fe24509544ba165265f33420ee4a
Author: Zhouyi Zhou <zhouzhouyi@gmail.com>
Date:   Mon Jul 26 05:43:33 2021 +0800

    rcu: Fix undefined Kconfig macros
    
    Invoking scripts/checkkconfigsymbols.py in the Linux-kernel source tree
    located the following issues:
    
    1. TREE_PREEMPT_RCU
    Referencing files: arch/sh/configs/sdk7786_defconfig
    
    It should now be CONFIG_PREEMPT_RCU. Except that the CONFIG_PREEMPT=y in
    that same file implies CONFIG_PREEMPT_RCU=y.  Therefore, delete the
    CONFIG_TREE_PREEMPT_RCU=y line.
    
    The reason is as follows:
    
    In kernel/rcu/Kconfig, we have
    config PREEMPT_RCU
            bool
            default y if PREEMPTION
    
    https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt says,
    "The default value is only assigned to the config symbol if no other value
     was set by the user (via the input prompt above)."
    there is no prompt in config PREEMPT_RCU entry, so we are guaranteed to
    get CONFIG_PREEMPT_RCU=y when CONFIG_PREEMPT is present.
    
    2. RCU_CPU_STALL_INFO
    Referencing files: arch/xtensa/configs/nommu_kc705_defconfig
    
    The old Kconfig option RCU_CPU_STALL_INFO was removed by commit
    75c27f119b64 ("rcu: Remove CONFIG_RCU_CPU_STALL_INFO"), and the kernel
    now acts as if this Kconfig option was unconditionally enabled.
    
    3. RCU_NOCB_CPU_ALL
    Referencing files:
    Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
    
    This is an old snapshot of the code. I update this from the real
    rcu_prepare_for_idle() function in kernel/rcu/tree_plugin.h.
    This change was tested by invoking "make htmldocs".
    
    4. RCU_TORTURE_TESTS
    Referencing files: kernel/rcu/rcutorture.c
    
    Forward-progress checking conflicts with CPU-stall testing, so we should
    complain at "modprobe rcutorture" when both are enabled.
    
    Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
index eeb351296df11..7fdf151a8680a 100644
--- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
+++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
@@ -202,49 +202,44 @@ newly arrived RCU callbacks against future grace periods:
     1 static void rcu_prepare_for_idle(void)
     2 {
     3   bool needwake;
-    4   struct rcu_data *rdp;
-    5   struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
-    6   struct rcu_node *rnp;
-    7   struct rcu_state *rsp;
-    8   int tne;
-    9
-   10   if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) ||
-   11       rcu_is_nocb_cpu(smp_processor_id()))
-   12     return;
+    4   struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+    5   struct rcu_node *rnp;
+    6   int tne;
+    7
+    8   lockdep_assert_irqs_disabled();
+    9   if (rcu_rdp_is_offloaded(rdp))
+   10     return;
+   11
+   12   /* Handle nohz enablement switches conservatively. */
    13   tne = READ_ONCE(tick_nohz_active);
-   14   if (tne != rdtp->tick_nohz_enabled_snap) {
-   15     if (rcu_cpu_has_callbacks(NULL))
-   16       invoke_rcu_core();
-   17     rdtp->tick_nohz_enabled_snap = tne;
+   14   if (tne != rdp->tick_nohz_enabled_snap) {
+   15     if (!rcu_segcblist_empty(&rdp->cblist))
+   16       invoke_rcu_core(); /* force nohz to see update. */
+   17     rdp->tick_nohz_enabled_snap = tne;
    18     return;
-   19   }
+   19	}
    20   if (!tne)
    21     return;
-   22   if (rdtp->all_lazy &&
-   23       rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
-   24     rdtp->all_lazy = false;
-   25     rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
-   26     invoke_rcu_core();
-   27     return;
-   28   }
-   29   if (rdtp->last_accelerate == jiffies)
-   30     return;
-   31   rdtp->last_accelerate = jiffies;
-   32   for_each_rcu_flavor(rsp) {
-   33     rdp = this_cpu_ptr(rsp->rda);
-   34     if (rcu_segcblist_pend_cbs(&rdp->cblist))
-   35       continue;
-   36     rnp = rdp->mynode;
-   37     raw_spin_lock_rcu_node(rnp);
-   38     needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
-   39     raw_spin_unlock_rcu_node(rnp);
-   40     if (needwake)
-   41       rcu_gp_kthread_wake(rsp);
-   42   }
-   43 }
+   22
+   23   /*
+   24    * If we have not yet accelerated this jiffy, accelerate all
+   25    * callbacks on this CPU.
+   26   */
+   27   if (rdp->last_accelerate == jiffies)
+   28     return;
+   29   rdp->last_accelerate = jiffies;
+   30   if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
+   31     rnp = rdp->mynode;
+   32     raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+   33     needwake = rcu_accelerate_cbs(rnp, rdp);
+   34     raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+   35     if (needwake)
+   36       rcu_gp_kthread_wake();
+   37   }
+   38 }
 
 But the only part of ``rcu_prepare_for_idle()`` that really matters for
-this discussion are lines 37–39. We will therefore abbreviate this
+this discussion are lines 32–34. We will therefore abbreviate this
 function as follows:
 
 .. kernel-figure:: rcu_node-lock.svg
diff --git a/arch/sh/configs/sdk7786_defconfig b/arch/sh/configs/sdk7786_defconfig
index f776a1d0d2776..a8662b6927ec7 100644
--- a/arch/sh/configs/sdk7786_defconfig
+++ b/arch/sh/configs/sdk7786_defconfig
@@ -5,7 +5,6 @@ CONFIG_BSD_PROCESS_ACCT=y
 CONFIG_BSD_PROCESS_ACCT_V3=y
 CONFIG_AUDIT=y
 CONFIG_AUDITSYSCALL=y
-CONFIG_TREE_PREEMPT_RCU=y
 CONFIG_RCU_TRACE=y
 CONFIG_IKCONFIG=y
 CONFIG_IKCONFIG_PROC=y
diff --git a/arch/xtensa/configs/nommu_kc705_defconfig b/arch/xtensa/configs/nommu_kc705_defconfig
index 88b2e222d4bff..fcb620ef37997 100644
--- a/arch/xtensa/configs/nommu_kc705_defconfig
+++ b/arch/xtensa/configs/nommu_kc705_defconfig
@@ -119,7 +119,6 @@ CONFIG_DEBUG_SPINLOCK=y
 CONFIG_DEBUG_MUTEXES=y
 CONFIG_DEBUG_ATOMIC_SLEEP=y
 CONFIG_STACKTRACE=y
-# CONFIG_RCU_CPU_STALL_INFO is not set
 CONFIG_RCU_TRACE=y
 # CONFIG_FTRACE is not set
 # CONFIG_LD_NO_RELAX is not set
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index ab4215266ebee..f640cbd9262c0 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2449,7 +2449,7 @@ static int __init rcu_torture_fwd_prog_init(void)
 	}
 	if (stall_cpu > 0) {
 		VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, conflicts with CPU-stall testing");
-		if (IS_MODULE(CONFIG_RCU_TORTURE_TESTS))
+		if (IS_MODULE(CONFIG_RCU_TORTURE_TEST))
 			return -EINVAL; /* In module, can fail back to user. */
 		WARN_ON(1); /* Make sure rcutorture notices conflict. */
 		return 0;