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>
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1 changed files with 4 additions and 8 deletions
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@ -15,6 +15,7 @@
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#include <linux/mc146818rtc.h>
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#include <linux/rtc.h>
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#include <linux/bcd.h>
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#include <linux/delay.h>
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#define RTC_PIE 0x40 /* periodic interrupt enable */
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#define RTC_AIE 0x20 /* alarm interrupt enable */
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@ -43,7 +44,6 @@ static inline unsigned char rtc_is_updating(void)
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static inline unsigned int get_rtc_time(struct rtc_time *time)
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{
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unsigned long uip_watchdog = jiffies;
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unsigned char ctrl;
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unsigned long flags;
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@ -53,19 +53,15 @@ static inline unsigned int get_rtc_time(struct rtc_time *time)
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/*
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* read RTC once any update in progress is done. The update
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* can take just over 2ms. We wait 10 to 20ms. There is no need to
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* can take just over 2ms. We wait 20ms. There is no need to
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* to poll-wait (up to 1s - eeccch) for the falling edge of RTC_UIP.
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* If you need to know *exactly* when a second has started, enable
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* periodic update complete interrupts, (via ioctl) and then
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* immediately read /dev/rtc which will block until you get the IRQ.
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* Once the read clears, read the RTC time (again via ioctl). Easy.
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*/
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if (rtc_is_updating() != 0)
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while (jiffies - uip_watchdog < 2*HZ/100) {
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barrier();
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cpu_relax();
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}
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if (rtc_is_updating())
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mdelay(20);
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/*
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* Only the values that we read from the RTC are set. We leave
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