[PATCH] use smp_mb/wmb/rmb where possible

Replace a number of memory barriers with smp_ variants.  This means we won't
take the unnecessary hit on UP machines.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/kthread.c

@@ -174,7 +174,7 @@ int kthread_stop(struct task_struct *k)
 
 	/* Must init completion *before* thread sees kthread_stop_info.k */
 	init_completion(&kthread_stop_info.done);
-	wmb();
+	smp_wmb();
 
 	/* Now set kthread_should_stop() to true, and wake it up. */
 	kthread_stop_info.k = k;

kernel/profile.c

@@ -522,7 +522,7 @@ static int __init create_hash_tables(void)
 	return 0;
 out_cleanup:
 	prof_on = 0;
-	mb();
+	smp_mb();
 	on_each_cpu(profile_nop, NULL, 0, 1);
 	for_each_online_cpu(cpu) {
 		struct page *page;

kernel/ptrace.c

@@ -135,7 +135,7 @@ int ptrace_attach(struct task_struct *task)
  	    (current->gid != task->sgid) ||
  	    (current->gid != task->gid)) && !capable(CAP_SYS_PTRACE))
 		goto bad;
-	rmb();
+	smp_rmb();
 	if (!task->mm->dumpable && !capable(CAP_SYS_PTRACE))
 		goto bad;
 	/* the same process cannot be attached many times */

kernel/stop_machine.c

@@ -33,7 +33,7 @@ static int stopmachine(void *cpu)
 	set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
 
 	/* Ack: we are alive */
-	mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
+	smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
 	atomic_inc(&stopmachine_thread_ack);
 
 	/* Simple state machine */
@@ -43,14 +43,14 @@ static int stopmachine(void *cpu)
 			local_irq_disable();
 			irqs_disabled = 1;
 			/* Ack: irqs disabled. */
-			mb(); /* Must read state first. */
+			smp_mb(); /* Must read state first. */
 			atomic_inc(&stopmachine_thread_ack);
 		} else if (stopmachine_state == STOPMACHINE_PREPARE
 			   && !prepared) {
 			/* Everyone is in place, hold CPU. */
 			preempt_disable();
 			prepared = 1;
-			mb(); /* Must read state first. */
+			smp_mb(); /* Must read state first. */
 			atomic_inc(&stopmachine_thread_ack);
 		}
 		/* Yield in first stage: migration threads need to
@@ -62,7 +62,7 @@ static int stopmachine(void *cpu)
 	}
 
 	/* Ack: we are exiting. */
-	mb(); /* Must read state first. */
+	smp_mb(); /* Must read state first. */
 	atomic_inc(&stopmachine_thread_ack);
 
 	if (irqs_disabled)
@@ -77,7 +77,7 @@ static int stopmachine(void *cpu)
 static void stopmachine_set_state(enum stopmachine_state state)
 {
 	atomic_set(&stopmachine_thread_ack, 0);
-	wmb();
+	smp_wmb();
 	stopmachine_state = state;
 	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
 		cpu_relax();

kernel/sys.c

@@ -525,7 +525,7 @@ asmlinkage long sys_setregid(gid_t rgid, gid_t egid)
 	if (new_egid != old_egid)
 	{
 		current->mm->dumpable = 0;
-		wmb();
+		smp_wmb();
 	}
 	if (rgid != (gid_t) -1 ||
 	    (egid != (gid_t) -1 && egid != old_rgid))
@@ -556,7 +556,7 @@ asmlinkage long sys_setgid(gid_t gid)
 		if(old_egid != gid)
 		{
 			current->mm->dumpable=0;
-			wmb();
+			smp_wmb();
 		}
 		current->gid = current->egid = current->sgid = current->fsgid = gid;
 	}
@@ -565,7 +565,7 @@ asmlinkage long sys_setgid(gid_t gid)
 		if(old_egid != gid)
 		{
 			current->mm->dumpable=0;
-			wmb();
+			smp_wmb();
 		}
 		current->egid = current->fsgid = gid;
 	}
@@ -596,7 +596,7 @@ static int set_user(uid_t new_ruid, int dumpclear)
 	if(dumpclear)
 	{
 		current->mm->dumpable = 0;
-		wmb();
+		smp_wmb();
 	}
 	current->uid = new_ruid;
 	return 0;
@@ -653,7 +653,7 @@ asmlinkage long sys_setreuid(uid_t ruid, uid_t euid)
 	if (new_euid != old_euid)
 	{
 		current->mm->dumpable=0;
-		wmb();
+		smp_wmb();
 	}
 	current->fsuid = current->euid = new_euid;
 	if (ruid != (uid_t) -1 ||
@@ -703,7 +703,7 @@ asmlinkage long sys_setuid(uid_t uid)
 	if (old_euid != uid)
 	{
 		current->mm->dumpable = 0;
-		wmb();
+		smp_wmb();
 	}
 	current->fsuid = current->euid = uid;
 	current->suid = new_suid;
@@ -748,7 +748,7 @@ asmlinkage long sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
 		if (euid != current->euid)
 		{
 			current->mm->dumpable = 0;
-			wmb();
+			smp_wmb();
 		}
 		current->euid = euid;
 	}
@@ -798,7 +798,7 @@ asmlinkage long sys_setresgid(gid_t rgid, gid_t egid, gid_t sgid)
 		if (egid != current->egid)
 		{
 			current->mm->dumpable = 0;
-			wmb();
+			smp_wmb();
 		}
 		current->egid = egid;
 	}
@@ -845,7 +845,7 @@ asmlinkage long sys_setfsuid(uid_t uid)
 		if (uid != old_fsuid)
 		{
 			current->mm->dumpable = 0;
-			wmb();
+			smp_wmb();
 		}
 		current->fsuid = uid;
 	}
@@ -875,7 +875,7 @@ asmlinkage long sys_setfsgid(gid_t gid)
 		if (gid != old_fsgid)
 		{
 			current->mm->dumpable = 0;
-			wmb();
+			smp_wmb();
 		}
 		current->fsgid = gid;
 		key_fsgid_changed(current);

kernel/timer.c

@@ -1007,7 +1007,7 @@ asmlinkage long sys_getppid(void)
 		 * Make sure we read the pid before re-reading the
 		 * parent pointer:
 		 */
-		rmb();
+		smp_rmb();
 		parent = me->group_leader->real_parent;
 		if (old != parent)
 			continue;