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SubjectRe: Total system lockup with Alt-SysRQ-L

Hi!

> We do have some tests in the do_exit() path to panic if/when init dies,
> which rely on the init PID being '1'. Unfortunately, these don't trigger
> because of the following bogosity in drivers/char/sysrq.c:
>
> if (p->pid == 1 && even_init)
> /* Ugly hack to kill init */
> p->pid = 0x8000;
>
> So, I propose we get rid of this "ugly hack", and the alt-sysrq-l
> option altogether - it would appear to serve no useful purpose.

Ask mj if it was ever usefull... But I guess it was not. Kill it.

>
> Here is a patch that does just this. It should apply to 2.4.17 and 2.5.1
> kernels fine (generated on 2.5.1).
>
> --- orig/drivers/char/sysrq.c Wed Dec 12 11:37:40 2001
> +++ linux/drivers/char/sysrq.c Mon Dec 24 12:19:58 2001
> @@ -284,24 +284,20 @@
>
> /* signal sysrq helper function
> * Sends a signal to all user processes */
> -static void send_sig_all(int sig, int even_init)
> +static void send_sig_all(int sig)
> {
> struct task_struct *p;
>
> for_each_task(p) {
> - if (p->mm) { /* Not swapper nor kernel thread */
> - if (p->pid == 1 && even_init)
> - /* Ugly hack to kill init */
> - p->pid = 0x8000;
> - if (p->pid != 1)
> - force_sig(sig, p);
> - }
> + if (p->mm && p->pid != 1)
> + /* Not swapper, init nor kernel thread */
> + force_sig(sig, p);
> }
> }
>
> static void sysrq_handle_term(int key, struct pt_regs *pt_regs,
> struct kbd_struct *kbd, struct tty_struct *tty) {
> - send_sig_all(SIGTERM, 0);
> + send_sig_all(SIGTERM);
> console_loglevel = 8;
> }
> static struct sysrq_key_op sysrq_term_op = {
> @@ -312,7 +308,7 @@
>
> static void sysrq_handle_kill(int key, struct pt_regs *pt_regs,
> struct kbd_struct *kbd, struct tty_struct *tty) {
> - send_sig_all(SIGKILL, 0);
> + send_sig_all(SIGKILL);
> console_loglevel = 8;
> }
> static struct sysrq_key_op sysrq_kill_op = {
> @@ -321,17 +317,6 @@
> action_msg: "Kill All Tasks",
> };
>
> -static void sysrq_handle_killall(int key, struct pt_regs *pt_regs,
> - struct kbd_struct *kbd, struct tty_struct *tty) {
> - send_sig_all(SIGKILL, 1);
> - console_loglevel = 8;
> -}
> -static struct sysrq_key_op sysrq_killall_op = {
> - handler: sysrq_handle_killall,
> - help_msg: "killalL",
> - action_msg: "Kill All Tasks (even init)",
> -};
> -
> /* END SIGNAL SYSRQ HANDLERS BLOCK */
>
>
> @@ -366,7 +351,7 @@
> #else
> /* k */ NULL,
> #endif
> -/* l */ &sysrq_killall_op,
> +/* l */ NULL,
> /* m */ &sysrq_showmem_op,
> /* n */ NULL,
> /* o */ NULL, /* This will often be registered
>
> --
> Russell King (rmk@arm.linux.org.uk) The developer of ARM Linux
> http://www.arm.linux.org.uk/personal/aboutme.html
>
> -
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