alpha: fix percpu build breakage

alpha percpu access requires custom SHIFT_PERCPU_PTR() definition for
modules to work around addressing range limitation.  This is done via
generating inline assembly using C preprocessing which forces the
assembler to generate external reference.  This happens behind the
compiler's back and makes the compiler think that static percpu variables
in modules are unused.

This used to be worked around by using __unused attribute for percpu
variables which prevent the compiler from omitting the variable; however,
recent declare/definition attribute unification change broke this as
__used can't be used for declaration.  Also, in the process,
PER_CPU_ATTRIBUTES definition in alpha percpu.h got broken.

This patch adds PER_CPU_DEF_ATTRIBUTES which is only used for definitions
and make alpha use it to add __used for percpu variables in modules.  This
also fixes the PER_CPU_ATTRIBUTES double definition bug.

Signed-off-by: Tejun Heo <tj@kernel.org>
Tested-by: maximilian attems <max@stro.at>
Acked-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 1 deletions

diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index d7d50d7ee51e..aa00800adacc 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -97,4 +97,8 @@ extern void setup_per_cpu_areas(void);
 #define PER_CPU_ATTRIBUTES
 #endif
 
+#ifndef PER_CPU_DEF_ATTRIBUTES
+#define PER_CPU_DEF_ATTRIBUTES
+#endif
+
 #endif /* _ASM_GENERIC_PERCPU_H_ */
diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
index 8f921d74f49f..68438e18fff4 100644
--- a/include/linux/percpu-defs.h
+++ b/include/linux/percpu-defs.h
@@ -24,7 +24,8 @@
 
 #define DEFINE_PER_CPU_SECTION(type, name, section)                     \
         __attribute__((__section__(PER_CPU_BASE_SECTION section)))      \
-        PER_CPU_ATTRIBUTES __typeof__(type) per_cpu__##name
+        PER_CPU_ATTRIBUTES PER_CPU_DEF_ATTRIBUTES                       \
+        __typeof__(type) per_cpu__##name
 
 /*
  * Variant on the per-CPU variable declaration/definition theme used for