diff -urN 2.3.51pre2/arch/alpha/kernel/alpha_ksyms.c rtc/arch/alpha/kernel/alpha_ksyms.c
--- 2.3.51pre2/arch/alpha/kernel/alpha_ksyms.c	Sun Feb 27 06:19:41 2000
+++ rtc/arch/alpha/kernel/alpha_ksyms.c	Fri Mar 10 04:58:33 2000
@@ -37,6 +37,7 @@
 extern void dump_thread(struct pt_regs *, struct user *);
 extern int dump_fpu(struct pt_regs *, elf_fpregset_t *);
 extern spinlock_t kernel_flag;
+extern spinlock_t rtc_lock;
 
 /* these are C runtime functions with special calling conventions: */
 extern void __divl (void);
@@ -201,6 +202,8 @@
 EXPORT_SYMBOL(__local_bh_count);
 EXPORT_SYMBOL(__local_irq_count);
 #endif /* __SMP__ */
+
+EXPORT_SYMBOL(rtc_lock);
 
 /*
  * The following are special because they're not called
diff -urN 2.3.51pre2/arch/alpha/kernel/time.c rtc/arch/alpha/kernel/time.c
--- 2.3.51pre2/arch/alpha/kernel/time.c	Fri Mar  3 02:19:23 2000
+++ rtc/arch/alpha/kernel/time.c	Fri Mar 10 04:57:56 2000
@@ -48,6 +48,7 @@
 
 static int set_rtc_mmss(unsigned long);
 
+spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;
 
 /*
  * Shift amount by which scaled_ticks_per_cycle is scaled.  Shifting
@@ -406,6 +407,8 @@
 	int real_seconds, real_minutes, cmos_minutes;
 	unsigned char save_control, save_freq_select;
 
+	/* irq are locally disabled here */
+	spin_lock(&rtc_lock);
 	/* Tell the clock it's being set */
 	save_control = CMOS_READ(RTC_CONTROL);
 	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
@@ -455,6 +458,7 @@
 	 */
 	CMOS_WRITE(save_control, RTC_CONTROL);
 	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
+	spin_unlock(&rtc_lock);
 
 	return retval;
 }
diff -urN 2.3.51pre2/arch/i386/kernel/i386_ksyms.c rtc/arch/i386/kernel/i386_ksyms.c
--- 2.3.51pre2/arch/i386/kernel/i386_ksyms.c	Sun Feb 27 06:19:41 2000
+++ rtc/arch/i386/kernel/i386_ksyms.c	Fri Mar 10 04:58:57 2000
@@ -25,6 +25,7 @@
 
 extern void dump_thread(struct pt_regs *, struct user *);
 extern int dump_fpu(elf_fpregset_t *);
+extern spinlock_t rtc_lock;
 
 #ifdef CONFIG_SMP
 extern void FASTCALL( __write_lock_failed(rwlock_t *rw));
@@ -145,3 +146,5 @@
 EXPORT_SYMBOL(get_wchan);
 
 EXPORT_SYMBOL(irq_stat);
+
+EXPORT_SYMBOL(rtc_lock);
diff -urN 2.3.51pre2/arch/i386/kernel/time.c rtc/arch/i386/kernel/time.c
--- 2.3.51pre2/arch/i386/kernel/time.c	Sun Jan 30 15:43:27 2000
+++ rtc/arch/i386/kernel/time.c	Fri Mar 10 04:57:56 2000
@@ -80,6 +80,8 @@
 
 extern rwlock_t xtime_lock;
 
+spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;
+
 static inline unsigned long do_fast_gettimeoffset(void)
 {
 	register unsigned long eax, edx;
@@ -302,6 +304,8 @@
 	int real_seconds, real_minutes, cmos_minutes;
 	unsigned char save_control, save_freq_select;
 
+	/* gets recalled with irq locally disabled */
+	spin_lock(&rtc_lock);
 	save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
 	CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);
 
@@ -347,6 +351,7 @@
 	 */
 	CMOS_WRITE(save_control, RTC_CONTROL);
 	CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);
+	spin_unlock(&rtc_lock);
 
 	return retval;
 }
diff -urN 2.3.51pre2/drivers/char/rtc.c rtc/drivers/char/rtc.c
--- 2.3.51pre2/drivers/char/rtc.c	Sun Feb 27 06:19:42 2000
+++ rtc/drivers/char/rtc.c	Fri Mar 10 05:01:20 2000
@@ -87,7 +87,7 @@
 
 static DECLARE_WAIT_QUEUE_HEAD(rtc_wait);
 
-static spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;
+extern spinlock_t rtc_lock;
 
 static struct timer_list rtc_irq_timer;
 
@@ -141,8 +141,11 @@
 #ifndef __alpha__
 /*
  *	A very tiny interrupt handler. It runs with SA_INTERRUPT set,
- *	so that there is no possibility of conflicting with the
- *	set_rtc_mmss() call that happens during some timer interrupts.
+ *	but there is possibility of conflicting with the set_rtc_mmss()
+ *	call (the rtc irq and the timer irq can easily run at the same
+ *	time in two different CPUs). So we need to serializes
+ *	accesses to the chip with the rtc_lock spinlock that each
+ *	architecture should implement in the timer code.
  *	(See ./arch/XXXX/kernel/time.c for the set_rtc_mmss() function.)
  */