[tip:core/rcu] srcu: Fix Kconfig botch when SRCU not selected

["tip-bot for Paul E. McKenney" <tipbot@zytor.com>]

Commit-ID:  677df9d4615a2db6774cd0e8951bf7404b858b3b
Gitweb:     http://git.kernel.org/tip/677df9d4615a2db6774cd0e8951bf7404b858b3b
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Sun, 23 Apr 2017 09:22:05 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 24 Apr 2017 08:14:48 +0200

srcu: Fix Kconfig botch when SRCU not selected

If the CONFIG_SRCU option is not selected, for example, when building
arch/tile allnoconfig, the following build errors appear:

	kernel/rcu/tree.o: In function `srcu_online_cpu':
	tree.c:(.text+0x4248): multiple definition of `srcu_online_cpu'
	kernel/rcu/srcutree.o:srcutree.c:(.text+0x2120): first defined here
	kernel/rcu/tree.o: In function `srcu_offline_cpu':
	tree.c:(.text+0x4250): multiple definition of `srcu_offline_cpu'
	kernel/rcu/srcutree.o:srcutree.c:(.text+0x2160): first defined here

The corresponding .config file shows CONFIG_TREE_SRCU=y, but no sign
of CONFIG_SRCU, which fatally confuses SRCU's #ifdefs, resulting in
the above errors.  The reason this occurs is the folowing line in
init/Kconfig's definition for TREE_SRCU:

	default y if !TINY_RCU && !CLASSIC_SRCU

If CONFIG_CLASSIC_SRCU=n, as it will be in for allnoconfig, and if
CONFIG_SMP=y, then we will get CONFIG_TREE_SRCU=y but no CONFIG_SRCU,
as seen in the .config file, and which will result in the above errors.
This error did not show up during rcutorture testing because rcutorture
forces CONFIG_SRCU=y, as it must to prevent build errors in rcutorture.c.

This commit therefore conditions TREE_SRCU (and TINY_SRCU, while it is
at it) with SRCU, like this:

	default y if SRCU && !TINY_RCU && !CLASSIC_SRCU

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20170423162205.GP3956@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 init/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 4119a44..fe72c12 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -545,13 +545,13 @@ config CLASSIC_SRCU
 
 config TINY_SRCU
 	bool
-	default y if TINY_RCU && !CLASSIC_SRCU
+	default y if SRCU && TINY_RCU && !CLASSIC_SRCU
 	help
 	  This option selects the single-CPU non-preemptible version of SRCU.
 
 config TREE_SRCU
 	bool
-	default y if !TINY_RCU && !CLASSIC_SRCU
+	default y if SRCU && !TINY_RCU && !CLASSIC_SRCU
 	help
 	  This option selects the full-fledged version of SRCU.