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Commit 940370fc authored by Yury Polyanskiy's avatar Yury Polyanskiy Committed by Linus Torvalds
Browse files

hangcheck-timer: fix x86_32 bugs 



drivers/char/hangcheck-timer.c is doubly broken.  When the overflown value
of TIMER_FREQ is abnormally low, it spams the syslog with KERN_CRIT
messages "Hangcheck: hangcheck value past margin!" But whether it happens
or not depends on HZ and lpj in a complex way.  People have hit it
occasionally as far as google search can tell.

First, the following line overflows unsigned long:

# define TIMER_FREQ (HZ*loops_per_jiffy)

Second, and more importantly, loops_per_jiffy has little to do with the
con= version from the the time scale of get_cycles() (aka rdtsc) to the
time scale of jiffies.

The attached patch resolves both of the problems.

Acked-by: default avatarJoel Becker <joel.becker@oracle.com>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Jan Glauber <jan.glauber@de.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b3b77c8c

drivers/char/hangcheck-timer.c

+14 −6
Original line number Diff line number Diff line
@@ -49,8 +49,9 @@ 
#include <asm/uaccess.h>

#include <linux/sysrq.h>

#include <linux/timer.h>

#include <linux/time.h>



#define VERSION_STR "0.9.0"

#define VERSION_STR "0.9.1"



#define DEFAULT_IOFENCE_MARGIN 60	/* Default fudge factor, in seconds */

#define DEFAULT_IOFENCE_TICK 180	/* Default timer timeout, in seconds */
@@ -119,10 +120,8 @@ __setup("hcheck_dump_tasks", hangcheck_parse_dump_tasks); 
#if defined(CONFIG_S390)

# define HAVE_MONOTONIC

# define TIMER_FREQ 1000000000ULL

#elif defined(CONFIG_IA64)

# define TIMER_FREQ ((unsigned long long)local_cpu_data->itc_freq)

#else

# define TIMER_FREQ (HZ*loops_per_jiffy)

# define TIMER_FREQ 1000000000ULL

#endif



#ifdef HAVE_MONOTONIC
@@ -130,7 +129,9 @@ extern unsigned long long monotonic_clock(void); 
#else

static inline unsigned long long monotonic_clock(void)

{

	return get_cycles();

	struct timespec ts;

	getrawmonotonic(&ts);

	return timespec_to_ns(&ts);

}

#endif  /* HAVE_MONOTONIC */
@@ -168,6 +169,13 @@ static void hangcheck_fire(unsigned long data) 
			printk(KERN_CRIT "Hangcheck: hangcheck value past margin!\n");

		}

	}

#if 0

	/*

	 * Enable to investigate delays in detail

	 */

	printk("Hangcheck: called %Ld ns since last time (%Ld ns overshoot)\n",

			tsc_diff, tsc_diff - hangcheck_tick*TIMER_FREQ);

#endif

	mod_timer(&hangcheck_ticktock, jiffies + (hangcheck_tick*HZ));

	hangcheck_tsc = monotonic_clock();

}
@@ -180,7 +188,7 @@ static int __init hangcheck_init(void) 
#if defined (HAVE_MONOTONIC)

	printk("Hangcheck: Using monotonic_clock().\n");

#else

	printk("Hangcheck: Using get_cycles().\n");

	printk("Hangcheck: Using getrawmonotonic().\n");

#endif  /* HAVE_MONOTONIC */

	hangcheck_tsc_margin =

		(unsigned long long)(hangcheck_margin + hangcheck_tick);