Re: Dumb question: BKL on reboot ?

[Hannes Reinecke <Hannes.Reinecke@suse.de>]

Andi Kleen wrote:
> Hannes Reinecke <Hannes.Reinecke@suse.de> writes:
> 
> 
>>I've got a dumb question: Why is the BKL held on entering sys_reboot()
>>in kernel/sys.c:405 ?
> 
> 
> Interesting. I have a few SMP deadlocks on x86-64 in reboot too 
> and it's possible that it is the same problem.
> 
> I would hold it during exection of the notifiers, but drop
> it before calling into machine_*
> 
Indeed. Works on s390 and survived several reboots (test still 
continuing). I moved lock_kernel() into the sections that actually _do_ 
something; looks much cleaner IMHO.

THX for your help.

Is it worth to try to push it into mainstream kernel?

Cheers,

Hannes
--

--- linux-2.4.21/kernel/sys.c.orig      2003-08-20 10:52:39.000000000 +0200
+++ linux-2.4.21/kernel/sys.c   2003-08-20 10:52:39.000000000 +0200
@@ -340,11 +340,12 @@
                         magic2 != LINUX_REBOOT_MAGIC2B))
                 return -EINVAL;

-       lock_kernel();
         switch (cmd) {
         case LINUX_REBOOT_CMD_RESTART:
+               lock_kernel();
                 notifier_call_chain(&reboot_notifier_list, SYS_RESTART, 
NULL);
                 printk(KERN_EMERG "Restarting system.\n");
+               unlock_kernel();
                 machine_restart(NULL);
                 break;

@@ -357,20 +358,25 @@
                 break;

         case LINUX_REBOOT_CMD_HALT:
+               lock_kernel();
                 notifier_call_chain(&reboot_notifier_list, SYS_HALT, NULL);
                 printk(KERN_EMERG "System halted.\n");
+               unlock_kernel();
                 machine_halt();
                 do_exit(0);
                 break;

         case LINUX_REBOOT_CMD_POWER_OFF:
+               lock_kernel();
                 notifier_call_chain(&reboot_notifier_list, 
SYS_POWER_OFF, NULL);
                 printk(KERN_EMERG "Power down.\n");
+               unlock_kernel();
                 machine_power_off();
                 do_exit(0);
                 break;

         case LINUX_REBOOT_CMD_RESTART2:
+               lock_kernel();
                 if (strncpy_from_user(&buffer[0], (char *)arg, 
sizeof(buffer) -
1) < 0) {
                         unlock_kernel();
                         return -EFAULT;
@@ -379,14 +385,13 @@

                 notifier_call_chain(&reboot_notifier_list, SYS_RESTART, 
buffer);
                 printk(KERN_EMERG "Restarting system with command 
'%s'.\n", buff
er);
+               unlock_kernel();
                 machine_restart(buffer);
                 break;

         default:
-               unlock_kernel();
                 return -EINVAL;
         }
-       unlock_kernel();
         return 0;
  }