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    Subject[PATCH] hangcheck-timer is broken on x86
    Dear Joel,

    The drivers/char/hangcheck-timer.c is doubly broken. 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 conversion from the
    the time scale of get_cycles() (aka rdtsc) to the time scale of jiffies.

    The attached patch resolves both of the problems.

    Best,
    Yury

    PS. I have CC-ed a few people who touched hangcheck-timer.c in 2006. Please CC me for follow-ups.

    diff --git a/drivers/char/hangcheck-timer.c b/drivers/char/hangcheck-timer.c
    index 712d9f2..c57a508 100644
    --- a/drivers/char/hangcheck-timer.c
    +++ b/drivers/char/hangcheck-timer.c
    @@ -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);[unhandled content-type:application/pgp-signature]
    \
     
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      Last update: 2010-03-24 04:53    [W:0.046 / U:32.560 seconds]
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