[RFC][PATCH 5/5] percpu: Add preempt checks back into this_cpu_read/write()

[Steven Rostedt <rostedt@goodmis.org>]

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From: Steven Rostedt <srostedt@redhat.com>

The conversion of per_cpu() and get_cpu_var() to this_cpu_read/write()
removed the debug check against using cpu variables in non atomic sections.

There are few cases where that is fine, but 99% of the time, if a per cpu
variable is going to be played with, it had better happen in an atomic
area, otherwise hard to find bugs may occur.

Right now only this_cpu_read/write() were updated. Maybe it would be a good
idea to handle the other this_cpu_*() functions as well.

Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/percpu.h |   17 +++++++++++++++--
 1 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 9ca008f..a4048de 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -22,6 +22,13 @@
 	 PERCPU_MODULE_RESERVE)
 #endif
 
+#ifdef CONFIG_DEBUG_PREEMPT
+# define debug_check_cpu() smp_processor_id()
+#else
+# define debug_check_cpu()
+#endif
+ 
+
 /*
  * Must be an lvalue. Since @var must be a simple identifier,
  * we force a syntax error here if it isn't.
@@ -342,7 +349,10 @@ do {									\
 # ifndef this_cpu_read_8
 #  define this_cpu_read_8(pcp)	_this_cpu_generic_read(pcp)
 # endif
-# define this_cpu_read(pcp)	__pcpu_size_call_return(this_cpu_read_, (pcp))
+# define this_cpu_read(pcp)	({					\
+			debug_check_cpu();				\
+			__pcpu_size_call_return(this_cpu_read_, (pcp));	\
+		})
 #endif
 
 #define _this_cpu_generic_to_op(pcp, val, op)				\
@@ -365,7 +375,10 @@ do {									\
 # ifndef this_cpu_write_8
 #  define this_cpu_write_8(pcp, val)	_this_cpu_generic_to_op((pcp), (val), =)
 # endif
-# define this_cpu_write(pcp, val)	__pcpu_size_call(this_cpu_write_, (pcp), (val))
+# define this_cpu_write(pcp, val)	({				\
+			debug_check_cpu();				\
+			__pcpu_size_call(this_cpu_write_, (pcp), (val)); \
+		})
 #endif
 
 #ifndef this_cpu_add
-- 
1.7.5.4