rcu: provide RCU options on non-preempt architectures too

Impact: build fix

Some old architectures still do not use kernel/Kconfig.preempt, so the
moving of the RCU options there broke their build:

 In file included from /home/mingo/tip/include/linux/sem.h:81,
                 from /home/mingo/tip/include/linux/sched.h:69,
                 from /home/mingo/tip/arch/alpha/kernel/asm-offsets.c:9:
 /home/mingo/tip/include/linux/rcupdate.h:62:2: error: #error "Unknown RCU implementation specified to kernel configuration"

Move these options back to init/Kconfig, which every architecture
includes.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

init/Kconfig

@@ -928,6 +928,80 @@ source "block/Kconfig"
 config PREEMPT_NOTIFIERS
 	bool
 
+choice
+	prompt "RCU Implementation"
+	default CLASSIC_RCU
+
+config CLASSIC_RCU
+	bool "Classic RCU"
+	help
+	  This option selects the classic RCU implementation that is
+	  designed for best read-side performance on non-realtime
+	  systems.
+
+	  Select this option if you are unsure.
+
+config TREE_RCU
+	bool "Tree-based hierarchical RCU"
+	help
+	  This option selects the RCU implementation that is
+	  designed for very large SMP system with hundreds or
+	  thousands of CPUs.
+
+config PREEMPT_RCU
+	bool "Preemptible RCU"
+	depends on PREEMPT
+	help
+	  This option reduces the latency of the kernel by making certain
+	  RCU sections preemptible. Normally RCU code is non-preemptible, if
+	  this option is selected then read-only RCU sections become
+	  preemptible. This helps latency, but may expose bugs due to
+	  now-naive assumptions about each RCU read-side critical section
+	  remaining on a given CPU through its execution.
+
+endchoice
+
+config RCU_TRACE
+	bool "Enable tracing for RCU"
+	depends on TREE_RCU || PREEMPT_RCU
+	help
+	  This option provides tracing in RCU which presents stats
+	  in debugfs for debugging RCU implementation.
+
+	  Say Y here if you want to enable RCU tracing
+	  Say N if you are unsure.
+
+config RCU_FANOUT
+	int "Tree-based hierarchical RCU fanout value"
+	range 2 64 if 64BIT
+	range 2 32 if !64BIT
+	depends on TREE_RCU
+	default 64 if 64BIT
+	default 32 if !64BIT
+	help
+	  This option controls the fanout of hierarchical implementations
+	  of RCU, allowing RCU to work efficiently on machines with
+	  large numbers of CPUs.  This value must be at least the cube
+	  root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit
+	  systems and up to 262,144 for 64-bit systems.
+
+	  Select a specific number if testing RCU itself.
+	  Take the default if unsure.
+
+config RCU_FANOUT_EXACT
+	bool "Disable tree-based hierarchical RCU auto-balancing"
+	depends on TREE_RCU
+	default n
+	help
+	  This option forces use of the exact RCU_FANOUT value specified,
+	  regardless of imbalances in the hierarchy.  This is useful for
+	  testing RCU itself, and might one day be useful on systems with
+	  strong NUMA behavior.
+
+	  Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
+
+	  Say N if unsure.
+
 config TREE_RCU_TRACE
 	def_bool RCU_TRACE && TREE_RCU
 	select DEBUG_FS

kernel/Kconfig.preempt

@@ -52,78 +52,3 @@ config PREEMPT
 
 endchoice
 
-choice
-	prompt "RCU Implementation"
-	default CLASSIC_RCU
-
-config CLASSIC_RCU
-	bool "Classic RCU"
-	help
-	  This option selects the classic RCU implementation that is
-	  designed for best read-side performance on non-realtime
-	  systems.
-
-	  Select this option if you are unsure.
-
-config TREE_RCU
-	bool "Tree-based hierarchical RCU"
-	help
-	  This option selects the RCU implementation that is
-	  designed for very large SMP system with hundreds or
-	  thousands of CPUs.
-
-config PREEMPT_RCU
-	bool "Preemptible RCU"
-	depends on PREEMPT
-	help
-	  This option reduces the latency of the kernel by making certain
-	  RCU sections preemptible. Normally RCU code is non-preemptible, if
-	  this option is selected then read-only RCU sections become
-	  preemptible. This helps latency, but may expose bugs due to
-	  now-naive assumptions about each RCU read-side critical section
-	  remaining on a given CPU through its execution.
-
-endchoice
-
-config RCU_TRACE
-	bool "Enable tracing for RCU"
-	depends on TREE_RCU || PREEMPT_RCU
-	help
-	  This option provides tracing in RCU which presents stats
-	  in debugfs for debugging RCU implementation.
-
-	  Say Y here if you want to enable RCU tracing
-	  Say N if you are unsure.
-
-config RCU_FANOUT
-	int "Tree-based hierarchical RCU fanout value"
-	range 2 64 if 64BIT
-	range 2 32 if !64BIT
-	depends on TREE_RCU
-	default 64 if 64BIT
-	default 32 if !64BIT
-	help
-	  This option controls the fanout of hierarchical implementations
-	  of RCU, allowing RCU to work efficiently on machines with
-	  large numbers of CPUs.  This value must be at least the cube
-	  root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit
-	  systems and up to 262,144 for 64-bit systems.
-
-	  Select a specific number if testing RCU itself.
-	  Take the default if unsure.
-
-config RCU_FANOUT_EXACT
-	bool "Disable tree-based hierarchical RCU auto-balancing"
-	depends on TREE_RCU
-	default n
-	help
-	  This option forces use of the exact RCU_FANOUT value specified,
-	  regardless of imbalances in the hierarchy.  This is useful for
-	  testing RCU itself, and might one day be useful on systems with
-	  strong NUMA behavior.
-
-	  Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
-
-	  Say n if unsure.
-
-