linux-kernel - [RESEND PATCH] jiffies.h: Declare jiffies and jiffies_64 with ____cacheline_aligned_in

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Date:   Mon,  3 Apr 2017 12:02:00 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     "Jason A . Donenfeld" <Jason@...c4.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Grant Grundler <grundler@...omium.org>,
        Michael Davidson <md@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: [RESEND PATCH] jiffies.h: Declare jiffies and jiffies_64 with ____cacheline_aligned_in_smp

jiffies_64 is defined in kernel/time/timer.c with ____cacheline_aligned_in_smp,
however this macro is not part of the declaration of jiffies and jiffies_64
in jiffies.h.

As a result clang generates the following warning:

kernel/time/timer.c:57:26: error: section does not match previous declaration [-Werror,-Wsection]
__visible u64 jiffies_64 __cacheline_aligned_in_smp = INITIAL_JIFFIES;
                         ^
include/linux/cache.h:39:36: note: expanded from macro '__cacheline_aligned_in_smp'
                                   ^
include/linux/cache.h:34:4: note: expanded from macro '__cacheline_aligned'
                 __section__(".data..cacheline_aligned")))
                 ^
include/linux/jiffies.h:77:12: note: previous attribute is here
extern u64 __jiffy_data jiffies_64;
           ^
include/linux/jiffies.h:70:38: note: expanded from macro '__jiffy_data'

Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
---
 include/linux/jiffies.h | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 624215cebee5..36872fbb815d 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -1,6 +1,7 @@
 #ifndef _LINUX_JIFFIES_H
 #define _LINUX_JIFFIES_H
 
+#include <linux/cache.h>
 #include <linux/math64.h>
 #include <linux/kernel.h>
 #include <linux/types.h>
@@ -63,19 +64,13 @@ extern int register_refined_jiffies(long clock_tick_rate);
 /* TICK_USEC is the time between ticks in usec assuming fake USER_HZ */
 #define TICK_USEC ((1000000UL + USER_HZ/2) / USER_HZ)
 
-/* some arch's have a small-data section that can be accessed register-relative
- * but that can only take up to, say, 4-byte variables. jiffies being part of
- * an 8-byte variable may not be correctly accessed unless we force the issue
- */
-#define __jiffy_data  __attribute__((section(".data")))
-
 /*
  * The 64-bit value is not atomic - you MUST NOT read it
  * without sampling the sequence number in jiffies_lock.
  * get_jiffies_64() will do this for you as appropriate.
  */
-extern u64 __jiffy_data jiffies_64;
-extern unsigned long volatile __jiffy_data jiffies;
+extern u64 __cacheline_aligned_in_smp jiffies_64;
+extern unsigned long volatile __cacheline_aligned_in_smp jiffies;
 
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void);
-- 
2.12.2.564.g063fe858b8-goog