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SubjectRe: [PATCH -mm] extend sysrq-p functionality to cover all CPUs
On Sun, 9 Mar 2008 22:14:58 -0400 Rik van Riel <riel@surriel.com> wrote:

> SysRP-P is not all that useful on SMP systems, since the sysrq
> irq rarely ends up on the CPU that we actually want to investigate.
>
> This patch extends sysrq-p to print a backtrace for every CPU,
> not just the lucky one that gets the sysrq irq. With this patch,
> "echo p > /proc/sysrq-trigger" does something useful.
>
> Signed-off-by: Rik van Riel <riel@redhat.com>
>
> diff -up linux-2.6.25-rc3-mm1/drivers/char/sysrq.c.multicpu linux-2.6.25-rc3-mm1/drivers/char/sysrq.c
> --- linux-2.6.25-rc3-mm1/drivers/char/sysrq.c.multicpu 2008-03-09 20:22:17.000000000 -0400
> +++ linux-2.6.25-rc3-mm1/drivers/char/sysrq.c 2008-03-09 21:54:02.000000000 -0400
> @@ -196,11 +196,29 @@ static struct sysrq_key_op sysrq_showloc
> #define sysrq_showlocks_op (*(struct sysrq_key_op *)0)
> #endif
>
> +static DEFINE_SPINLOCK(show_lock);
> +static void showacpu(void *dummy)
> +{
> + struct pt_regs *regs = get_irq_regs();
> +
> + spin_lock(&show_lock);
> + printk("CPU%d:\n", smp_processor_id());
> + show_stack(NULL, NULL);
> + spin_unlock(&show_lock);
> +}
> +static void sysrq_showregs_othercpus(struct work_struct *dummy)
> +{
> + smp_call_function(showacpu, NULL, 0, 0);
> +}
> +static DECLARE_WORK(sysrq_showregs, sysrq_showregs_othercpus);
> static void sysrq_handle_showregs(int key, struct tty_struct *tty)
> {
> struct pt_regs *regs = get_irq_regs();
> - if (regs)
> + if (regs) {
> + printk("CPU%d:\n", smp_processor_id());
> show_regs(regs);
> + }
> + schedule_work(&sysrq_showregs);
> }
> static struct sysrq_key_op sysrq_showregs_op = {
> .handler = sysrq_handle_showregs,

Doesn't everyone have a copy of this somewhere? ;)

However it does have the downside that info can scroll away on large cpu
counts. Maybe it should be a new sysrq command?



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