Re: Total system lockup with Alt-SysRQ-L

[Pavel Machek <pavel@suse.cz>]

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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