Provide a means to trap usages of per_cpu variables before
the per_cpu_areas are setup. Define CONFIG_DEBUG_PER_CPU to activate.

Signed-off-by: Mike Travis
---
include/asm-generic/percpu.h | 11 ++++++++++-
lib/Kconfig.debug | 12 ++++++++++++
2 files changed, 22 insertions(+), 1 deletion(-)

--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -47,12 +47,21 @@ extern unsigned long __per_cpu_offset[NR
#endif

/*
- * A percpu variable may point to a discarded reghions. The following are
+ * A percpu variable may point to a discarded regions. The following are
* established ways to produce a usable pointer from the percpu variable
* offset.
*/
+#ifdef CONFIG_DEBUG_PER_CPU
+#define per_cpu(var, cpu) (*({ \
+ if(!per_cpu_offset(cpu)) { \
+ printk("KERN_NOTICE per_cpu(%s,%d): not available!\n", #var, (int)cpu); \
+ BUG(); \
+ } \
+ SHIFT_PERCPU_PTR(&per_cpu_var(var), per_cpu_offset(cpu));}))
+#else
#define per_cpu(var, cpu) \
(*SHIFT_PERCPU_PTR(&per_cpu_var(var), per_cpu_offset(cpu)))
+#endif
#define __get_cpu_var(var) \
(*SHIFT_PERCPU_PTR(&per_cpu_var(var), my_cpu_offset))
#define __raw_get_cpu_var(var) \
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -610,6 +610,18 @@ config PROVIDE_OHCI1394_DMA_INIT

See Documentation/debugging-via-ohci1394.txt for more information.

+config DEBUG_PER_CPU
+ bool "Debug per_cpu usage"
+ depends on DEBUG_KERNEL
+ depends on SMP
+ default n
+ help
+ Say Y here to add code that verifies the per_cpu area is
+ setup before accessing a per_cpu variable. It does add a
+ significant amount of code to kernel memory.
+
+ If unsure, say N.
+
source "samples/Kconfig"

source "lib/Kconfig.kgdb"

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