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Subject[patch 34/71] rtc: fix deadlock
2.6.26-stable review patch.  If anyone has any objections, please let us
know.

------------------
From: Ingo Molnar <mingo@elte.hu>
commit 38c052f8cff1bd323ccfa968136a9556652ee420 upstream

if get_rtc_time() is _ever_ called with IRQs off, we deadlock badly
in it, waiting for jiffies to increment.

So make the code more robust by doing an explicit mdelay(20).

This solves a very hard to reproduce/debug hard lockup reported
by Mikael Pettersson.

Reported-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/asm-generic/rtc.h | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)
--- a/include/asm-generic/rtc.h
+++ b/include/asm-generic/rtc.h
@@ -15,6 +15,7 @@
#include <linux/mc146818rtc.h>
#include <linux/rtc.h>
#include <linux/bcd.h>
+#include <linux/delay.h>

#define RTC_PIE 0x40 /* periodic interrupt enable */
#define RTC_AIE 0x20 /* alarm interrupt enable */
@@ -43,7 +44,6 @@ static inline unsigned char rtc_is_updat

static inline unsigned int get_rtc_time(struct rtc_time *time)
{
- unsigned long uip_watchdog = jiffies;
unsigned char ctrl;
unsigned long flags;

@@ -53,19 +53,15 @@ static inline unsigned int get_rtc_time(

/*
* read RTC once any update in progress is done. The update
- * can take just over 2ms. We wait 10 to 20ms. There is no need to
+ * can take just over 2ms. We wait 20ms. There is no need to
* to poll-wait (up to 1s - eeccch) for the falling edge of RTC_UIP.
* If you need to know *exactly* when a second has started, enable
* periodic update complete interrupts, (via ioctl) and then
* immediately read /dev/rtc which will block until you get the IRQ.
* Once the read clears, read the RTC time (again via ioctl). Easy.
*/
-
- if (rtc_is_updating() != 0)
- while (jiffies - uip_watchdog < 2*HZ/100) {
- barrier();
- cpu_relax();
- }
+ if (rtc_is_updating())
+ mdelay(20);

/*
* Only the values that we read from the RTC are set. We leave
--


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