[PATCH] timer initialisation fix

We need the boot CPU's tvec_bases[] entry to be initialised super-early in
boot, for early_serial_setup().  That runs within setup_arch(), before even
per-cpu areas are initialised.

The patch changes tvec_bases to use compile-time initialisation, and adds a
separate array `tvec_base_done' to keep track of which CPU has had its
tvec_bases[] entry initialised (because we can no longer use the zeroness of
that tvec_bases[] entry to determine whether it has been initialised).

Thanks to Eugene Surovegin <ebs@ebshome.net> for diagnosing this.

Cc: Eugene Surovegin <ebs@ebshome.net>
Cc: Jan Beulich <jbeulich@novell.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/timer.c

@@ -81,9 +81,10 @@ struct tvec_t_base_s {
 } ____cacheline_aligned_in_smp;
 
 typedef struct tvec_t_base_s tvec_base_t;
-static DEFINE_PER_CPU(tvec_base_t *, tvec_bases);
+
 tvec_base_t boot_tvec_bases;
 EXPORT_SYMBOL(boot_tvec_bases);
+static DEFINE_PER_CPU(tvec_base_t *, tvec_bases) = { &boot_tvec_bases };
 
 static inline void set_running_timer(tvec_base_t *base,
 					struct timer_list *timer)
@@ -1224,28 +1225,36 @@ static int __devinit init_timers_cpu(int cpu)
 {
 	int j;
 	tvec_base_t *base;
+	static char __devinitdata tvec_base_done[NR_CPUS];
 
-	base = per_cpu(tvec_bases, cpu);
-	if (!base) {
+	if (!tvec_base_done[cpu]) {
 		static char boot_done;
 
-		/*
-		 * Cannot do allocation in init_timers as that runs before the
-		 * allocator initializes (and would waste memory if there are
-		 * more possible CPUs than will ever be installed/brought up).
-		 */
 		if (boot_done) {
+			/*
+			 * The APs use this path later in boot
+			 */
 			base = kmalloc_node(sizeof(*base), GFP_KERNEL,
 						cpu_to_node(cpu));
 			if (!base)
 				return -ENOMEM;
 			memset(base, 0, sizeof(*base));
+			per_cpu(tvec_bases, cpu) = base;
 		} else {
-			base = &boot_tvec_bases;
+			/*
+			 * This is for the boot CPU - we use compile-time
+			 * static initialisation because per-cpu memory isn't
+			 * ready yet and because the memory allocators are not
+			 * initialised either.
+			 */
 			boot_done = 1;
+			base = &boot_tvec_bases;
 		}
-		per_cpu(tvec_bases, cpu) = base;
+		tvec_base_done[cpu] = 1;
+	} else {
+		base = per_cpu(tvec_bases, cpu);
 	}
+
 	spin_lock_init(&base->lock);
 	for (j = 0; j < TVN_SIZE; j++) {
 		INIT_LIST_HEAD(base->tv5.vec + j);