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SubjectRe: [PATCH v2 1/2] tty/sysrq: Make sysrq handler NMI aware
Hi,

On Thu, Mar 3, 2022 at 10:45 PM Hitomi Hasegawa
<hasegawa-hitomi@fujitsu.com> wrote:
>
> void __handle_sysrq(int key, bool check_mask)
> {
> const struct sysrq_key_op *op_p;
> @@ -573,6 +606,10 @@ void __handle_sysrq(int key, bool check_mask)
> int orig_suppress_printk;
> int i;
>
> + /* Skip sysrq handling if one already in progress */
> + if (sysrq_nmi_key != -1)
> + return;

Should this give a warning?

Also, can you remind me why this is safe if two CPUs both call
handle_sysrq() at the same time? Can't both of them make it past this?
That doesn't seem so great.


> @@ -596,7 +633,13 @@ void __handle_sysrq(int key, bool check_mask)
> if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
> pr_info("%s\n", op_p->action_msg);
> console_loglevel = orig_log_level;
> - op_p->handler(key);
> +
> + if (in_nmi() && !op_p->nmi_safe) {
> + sysrq_nmi_key = key;
> + irq_work_queue(&sysrq_irq_work);

It looks like irq_work_queue() returns false if it fails to queue.
Maybe it's worth checking and setting "sysrq_nmi_key" back to -1 if it
fails?

-Doug

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