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    SubjectRe: [PATCH] softlockup: fix problem with long kernel pauses fromkgdb
    Ingo Molnar wrote:
    > * Jason Wessel <jason.wessel@windriver.com> wrote:
    >
    >> -----
    >> From: Jason Wessel <jason.wessel@windriver.com>
    >> Subject: [PATCH] softlockup: add sched_clock_tick() to avoid kernel warning on kgdb resume
    >>
    >> When CONFIG_HAVE_UNSTABLE_SCHED_CLOCK is set sched_clock() gets the
    >> time from hardware, such as from TSC. In this configuration kgdb will
    >> report a softlock warning messages on resuming or detaching from a
    >> debug session.
    >>
    >
    > Hm, this looks quite ugly. Peter, Thomas, can you think of a cleaner
    > solution?
    >

    Below was a more specific test case I received from Dongdong Deng
    which did not require kgdb. The test case is not something to merge,
    it is just a simple module to build to demonstrate the problem outside
    of kgdb.

    The patch I submitted might have been on the "ugly" side, but there
    was not an obvious way to solve the problem without making changes in
    kernel/sched*. I opted for something that was entirely self contained
    to the softlockup code.

    Jason.

    ============= test case ================
    /* Information about this test case.
    * -------------------------------------
    * 1: CONFIG_HAVE_UNSTABLE_SCHED_CLOCK=y
    *
    * 2: export clocksource_touch_watchdog for this test case to build.
    *
    *
    * diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
    * index 7466cb8..c81f9a3 100644
    * --- a/kernel/time/clocksource.c
    * +++ b/kernel/time/clocksource.c
    * @@ -319,6 +319,7 @@ void clocksource_touch_watchdog(void)
    * {
    * clocksource_resume_watchdog();
    * }
    * +EXPORT_SYMBOL(clocksource_touch_watchdog);
    *
    * 3: build following module, insmod and observe the softlockup
    * warning or watch your system reboot if you have reboot
    * on softlockup set.
    *
    */
    #include <linux/module.h>
    #include <linux/init.h>
    #include <linux/irqflags.h>
    #include <linux/delay.h>
    #include <linux/sched.h>
    #include <linux/clocksource.h>



    static int example_init(void)
    {
    unsigned long flags;
    unsigned i;
    printk(KERN_NOTICE"softlockup test init\n");

    local_irq_save(flags);

    for (i = 0; i < 70; i++)
    mdelay(1000);

    touch_softlockup_watchdog();
    clocksource_touch_watchdog();

    local_irq_restore(flags);

    return 0;
    }
    static void example_exit(void)
    {
    printk(KERN_NOTICE"softlockup test exit\n");
    }
    module_init(example_init);
    module_exit(example_exit);
    MODULE_LICENSE("GPL");



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