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rtc: fix deadlock 

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>
This commit is contained in:
Ingo Molnar 2008-08-23 17:59:07 +02:00
parent 3c4fbe5e01
commit 38c052f8cf
1 changed files with 4 additions and 8 deletions
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12
include/asm-generic/rtc.h
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@ -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_updating(void)
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(struct rtc_time *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