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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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