[PATCH][2.5] Remove BUG in cpu_up

[PATCH][2.5] Remove BUG in cpu_up

[Zwane Mwaikambo]

I think a BUG here is a bit on the extreme side, we already have a running 
processor (in boot i'd presume its the BSP) so we can afford to limp on. 
At runtime a stopped/dead processor which refuses to come back up 
shouldn't make the kernel oops.

	Zwane

Index: linux-2.5.47/kernel/cpu.c
===================================================================
RCS file: /build/cvsroot/linux-2.5.47/kernel/cpu.c,v
retrieving revision 1.1.1.1
diff -u -r1.1.1.1 cpu.c
--- linux-2.5.47/kernel/cpu.c	11 Nov 2002 03:59:33 -0000	1.1.1.1
+++ linux-2.5.47/kernel/cpu.c	13 Nov 2002 03:37:37 -0000
@@ -35,13 +35,11 @@
 		return ret;
 
 	if (cpu_online(cpu)) {
-		ret = -EINVAL;
+		ret = -EBUSY;
 		goto out;
 	}
 	ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 	if (ret == NOTIFY_BAD) {
-		printk("%s: attempt to bring up CPU %u failed\n",
-				__FUNCTION__, cpu);
 		ret = -EINVAL;
 		goto out_notify;
 	}
@@ -50,16 +48,22 @@
 	ret = __cpu_up(cpu);
 	if (ret != 0)
 		goto out_notify;
-	if (!cpu_online(cpu))
-		BUG();
+
+	if (!cpu_online(cpu)) {
+		ret = -EIO;
+		goto out_notify;
+	}
 
 	/* Now call notifier in preparation. */
-	printk("CPU %u IS NOW UP!\n", cpu);
+	printk(KERN_INFO "CPU %u IS NOW UP!\n", cpu);
 	notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 
 out_notify:
-	if (ret != 0)
+	if (ret != 0) {
+		printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n",
+			__FUNCTION__, cpu);
 		notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
+	}
 out:
 	up(&cpucontrol);
 	return ret;
-- 
function.linuxpower.ca

Re: [PATCH][2.5] Remove BUG in cpu_up

[Rusty Russell]

In message <Pine.LNX.4.44.0211122236270.24523-100000@montezuma.mastecende.com> 
you write:
>  	ret = __cpu_up(cpu);
>  	if (ret != 0)
>  		goto out_notify;
> -	if (!cpu_online(cpu))
> -		BUG();
> +
> +	if (!cpu_online(cpu)) {
> +		ret = -EIO;
> +		goto out_notify;
> +	}

Err, no.  If __cpu_up(cpu) succeeded, that means the cpu should bloody
well be online!

Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: [PATCH][2.5] Remove BUG in cpu_up

[Zwane Mwaikambo]

On Wed, 13 Nov 2002, Rusty Russell wrote:

> Err, no.  If __cpu_up(cpu) succeeded, that means the cpu should bloody
> well be online!

smp startup looks rather convoluted to me right now, but if i see it 
correctly, __cpu_up should eventually be doing a wakeup_secondary_via_INIT 
on vanilla i386 correct? In that case, the processor accepting the IPI 
doesn't necessarily mean it will have managed to initialise (if at all) itself by 
the time you do that cpu_online check, the wakeup_secondary_via_INIT will 
simply tell you wether you succeeded in sending the IPI. There are i386 
systems which take considerably long to do that AP initialisation 
procedure. I still reckon the most you should do there is specify 
PENDING with the cpu in question sending an ONLINE notification when it 
finally does all init.

	Zwane

-- 
function.linuxpower.ca

Re: [PATCH][2.5] Remove BUG in cpu_up

[Rusty Russell]

In message <Pine.LNX.4.44.0211130804380.24523-100000@montezuma.mastecende.com> 
you write:
> On Wed, 13 Nov 2002, Rusty Russell wrote:
> 
> > Err, no.  If __cpu_up(cpu) succeeded, that means the cpu should bloody
> > well be online!
> 
> smp startup looks rather convoluted to me right now, but if i see it 
> correctly, __cpu_up should eventually be doing a wakeup_secondary_via_INIT 
> on vanilla i386 correct? In that case, the processor accepting the IPI 
> doesn't necessarily mean it will have managed to initialise (if at all) itsel
f by 

It is bloody convoluted.  Hmm, the arch needs to wait before returning
"success" on __cpu_up.

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: [PATCH][2.5] Remove BUG in cpu_up

[Zwane Mwaikambo]

On Thu, 14 Nov 2002, Rusty Russell wrote:

> It is bloody convoluted.  Hmm, the arch needs to wait before returning
> "success" on __cpu_up.

What if the processor never comes up? Whats wrong with doing this async?

	Zwane
-- 
function.linuxpower.ca

Re: [PATCH][2.5] Remove BUG in cpu_up

[Rusty Russell]

In message <Pine.LNX.4.44.0211132217580.24523-100000@montezuma.mastecende.com> 
you write:
> On Thu, 14 Nov 2002, Rusty Russell wrote:
> 
> > It is bloody convoluted.  Hmm, the arch needs to wait before returning
> > "success" on __cpu_up.
> 
> What if the processor never comes up? Whats wrong with doing this async?

What's wrong with doing it sync?  Are you in a hurry? 8)

That's what the return code is *for*...
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: [PATCH][2.5] Remove BUG in cpu_up

[Zwane Mwaikambo]

On Thu, 14 Nov 2002, Rusty Russell wrote:

> What's wrong with doing it sync?  Are you in a hurry? 8)
> 
> That's what the return code is *for*...
> Rusty.

Yes, i'd rather a box limp along until i can come up with a solution 
rather than it sit there indefinitely waiting for a processor which has 
decided to go on early retirement ;)

But i feel like i'm going round in circles, anyone else with opinions on 
this?

	Zwane
-- 
function.linuxpower.ca