Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
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>
+4
-8
include/asm-generic/rtc.h
+4
-8
include/asm-generic/rtc.h
···
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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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static inline unsigned int get_rtc_time(struct rtc_time *time)
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{
47
-
unsigned long uip_watchdog = jiffies;
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unsigned char ctrl;
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unsigned long flags;
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···
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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
56
+
* 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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-
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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