[PATCH] lockdep: HPET/RTC fix

Joseph Fannin reported that hpet_rtc_interrupt() enables hardirqs
in irq context:

[ 25.628000] [<c014af4e>] trace_hardirqs_on+0xce/0x200
[ 25.628000] [<c036cf21>] _spin_unlock_irq+0x31/0x70
[ 25.628000] [<c0296584>] rtc_get_rtc_time+0x44/0x1a0
[ 25.628000] [<c01198bb>] hpet_rtc_interrupt+0x21b/0x280
[ 25.628000] [<c0161141>] handle_IRQ_event+0x31/0x70
[ 25.628000] [<c0162d37>] handle_edge_irq+0xe7/0x210
[ 25.628000] [<c0106192>] do_IRQ+0x92/0x120
[ 25.628000] [<c0104121>] common_interrupt+0x25/0x2c

the call of rtc_get_rtc_time() is highly suspect. At a minimum we
need the patch below to save/restore hardirq state.

Signed-off-by: Ingo Molnar <[e-mail]>
Cc: Joseph Fannin <[e-mail]>
Cc: John Stultz <[e-mail]>
Cc: Arjan van de Ven <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/rtc.c

···
 
 void rtc_get_rtc_time(struct rtc_time *rtc_tm)
 {
-	unsigned long uip_watchdog = jiffies;
+	unsigned long uip_watchdog = jiffies, flags;
 	unsigned char ctrl;
 #ifdef CONFIG_MACH_DECSTATION
 	unsigned int real_year;
···
 	 * RTC has RTC_DAY_OF_WEEK, we should usually ignore it, as it is
 	 * only updated by the RTC when initially set to a non-zero value.
 	 */
-	spin_lock_irq(&rtc_lock);
+	spin_lock_irqsave(&rtc_lock, flags);
 	rtc_tm->tm_sec = CMOS_READ(RTC_SECONDS);
 	rtc_tm->tm_min = CMOS_READ(RTC_MINUTES);
 	rtc_tm->tm_hour = CMOS_READ(RTC_HOURS);
···
 	real_year = CMOS_READ(RTC_DEC_YEAR);
 #endif
 	ctrl = CMOS_READ(RTC_CONTROL);
-	spin_unlock_irq(&rtc_lock);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
 	{