Re: stable-rc/linux-3.18.y build: 184 builds: 3 failed, 181 passed, 3 errors (v3.18.86-23-g635374e30005)

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Dec 06, 2017 at 09:56:36PM +0100, Arnd Bergmann wrote:
> On Wed, Dec 6, 2017 at 8:24 PM, kernelci.org bot <bot@kernelci.org> wrote:
> >
> > stable-rc/linux-3.18.y build: 184 builds: 3 failed, 181 passed, 3 errors (v3.18.86-23-g635374e30005)
> > Full Build Summary: https://kernelci.org/build/stable-rc/branch/linux-3.18.y/kernel/v3.18.86-23-g635374e30005/
> > Tree: stable-rc
> > Branch: linux-3.18.y
> > Git Describe: v3.18.86-23-g635374e30005
> > Git Commit: 635374e300051ce71a548aff2c469fbda3910c21
> > Git URL: http://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
> > Built: 4 unique architectures
> >
> > Build Failures Detected:
> >
> > x86: gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.4)
> > defconfig+CONFIG_LKDTM=y FAIL
> > i386_defconfig FAIL
> > x86_64_defconfig FAIL
> >
> > Errors Detected:
> >
> > x86: gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.4)
> > defconfig+CONFIG_LKDTM=y 1 error
> > i386_defconfig 1 error
> > x86_64_defconfig 1 error
> > Errors summary:
> > 2 kprobes.c:(.text+0x91f42): undefined reference to `synchronize_rcu_tasks'
> > 1 kprobes.c:(.text+0x80dc8): undefined reference to `synchronize_rcu_tasks'
> 
> Same as v4.9, caused by 98efb31592b4 ("kprobes: Use synchronize_rcu_tasks()
>  for optprobe with CONFIG_PREEMPT=y").

Looks to me like they are both missing 7e42776d5ed1f ("rcu: Drive
TASKS_RCU directly off of PREEMPT"), which is shown below.

Masami, how would you like to proceed?

							Thanx, Paul

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

commit 7e42776d5ed1fe9a941ed8876c5d15cd7cf5d89f
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date:   Thu May 25 08:05:00 2017 -0700

    rcu: Drive TASKS_RCU directly off of PREEMPT
    
    The actual use of TASKS_RCU is only when PREEMPT, otherwise RCU-sched
    is used instead.  This commit therefore makes synchronize_rcu_tasks()
    and call_rcu_tasks() available always, but mapped to synchronize_sched()
    and call_rcu_sched(), respectively, when !PREEMPT.  This approach also
    allows some #ifdefs to be removed from rcutorture.
    
    Reported-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
    Acked-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f816fc72b51e..c3f380befdd7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -58,8 +58,6 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func);
 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func);
 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func);
 void synchronize_sched(void);
-void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
-void synchronize_rcu_tasks(void);
 void rcu_barrier_tasks(void);
 
 #ifdef CONFIG_PREEMPT_RCU
@@ -176,10 +174,14 @@ extern struct srcu_struct tasks_rcu_exit_srcu;
 		rcu_all_qs(); \
 		rcu_note_voluntary_context_switch_lite(t); \
 	} while (0)
+void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
+void synchronize_rcu_tasks(void);
 #else /* #ifdef CONFIG_TASKS_RCU */
 #define TASKS_RCU(x) do { } while (0)
 #define rcu_note_voluntary_context_switch_lite(t)	do { } while (0)
 #define rcu_note_voluntary_context_switch(t)		rcu_all_qs()
+#define call_rcu_tasks call_rcu_sched
+#define synchronize_rcu_tasks synchronize_sched
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
 /**
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index be90c945063f..9210379c0353 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -69,8 +69,7 @@ config TREE_SRCU
 	  This option selects the full-fledged version of SRCU.
 
 config TASKS_RCU
-	bool
-	default n
+	def_bool PREEMPT
 	select SRCU
 	help
 	  This option enables a task-based RCU implementation that uses
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index b8f7f8ce8575..b284c861a511 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -696,8 +696,6 @@ static struct rcu_torture_ops sched_ops = {
 	.name		= "sched"
 };
 
-#ifdef CONFIG_TASKS_RCU
-
 /*
  * Definitions for RCU-tasks torture testing.
  */
@@ -735,24 +733,11 @@ static struct rcu_torture_ops tasks_ops = {
 	.name		= "tasks"
 };
 
-#define RCUTORTURE_TASKS_OPS &tasks_ops,
-
 static bool __maybe_unused torturing_tasks(void)
 {
 	return cur_ops == &tasks_ops;
 }
 
-#else /* #ifdef CONFIG_TASKS_RCU */
-
-#define RCUTORTURE_TASKS_OPS
-
-static bool __maybe_unused torturing_tasks(void)
-{
-	return false;
-}
-
-#endif /* #else #ifdef CONFIG_TASKS_RCU */
-
 /*
  * RCU torture priority-boost testing.  Runs one real-time thread per
  * CPU for moderate bursts, repeatedly registering RCU callbacks and
@@ -1749,7 +1734,7 @@ rcu_torture_init(void)
 	int firsterr = 0;
 	static struct rcu_torture_ops *torture_ops[] = {
 		&rcu_ops, &rcu_bh_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,
-		&sched_ops, RCUTORTURE_TASKS_OPS
+		&sched_ops, &tasks_ops,
 	};
 
 	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
diff --git a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
index 9ad3f89c8dc7..af6fca03602f 100644
--- a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
+++ b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
@@ -69,11 +69,11 @@ CONFIG_RCU_TORTURE_TEST_RUNNABLE
 CONFIG_PREEMPT_RCU
 CONFIG_TREE_RCU
 CONFIG_TINY_RCU
+CONFIG_TASKS_RCU
 
 	These are controlled by CONFIG_PREEMPT and/or CONFIG_SMP.
 
 CONFIG_SRCU
-CONFIG_TASKS_RCU
 
 	Selected by CONFIG_RCU_TORTURE_TEST, so cannot disable.