ipc/sem.c: cacheline align the ipc spinlock for semaphores

Cacheline align the spinlock for sysv semaphores.  Without the patch, the
spinlock and sem_otime [written by every semop that modified the array]
and sem_base [read in the hot path of try_atomic_semop()] can be in the
same cacheline.

Signed-off-by: Manfred Spraul <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Zach Brown <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/sem.h

@@ -79,6 +79,7 @@ struct  seminfo {
 #ifdef __KERNEL__
 #include <asm/atomic.h>
 #include <linux/rcupdate.h>
+#include <linux/cache.h>
 
 struct task_struct;
 
@@ -91,7 +92,8 @@ struct sem {
 
 /* One sem_array data structure for each set of semaphores in the system. */
 struct sem_array {
-	struct kern_ipc_perm	sem_perm;	/* permissions .. see ipc.h */
+	struct kern_ipc_perm	____cacheline_aligned_in_smp
+				sem_perm;	/* permissions .. see ipc.h */
 	time_t			sem_otime;	/* last semop time */
 	time_t			sem_ctime;	/* last change time */
 	struct sem		*sem_base;	/* ptr to first semaphore in array */