linux-kernel - Re: [PATCH 2/3] stop

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Date:	Tue, 8 Jul 2008 23:11:35 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Akinobu Mita" <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org, "Jason Baron" <jbaron@...hat.com>,
	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>,
	"Max Krasnyansky" <maxk@...lcomm.com>,
	"Hidetoshi Seto" <seto.hidetoshi@...fujitsu.com>
Subject: Re: [PATCH 2/3] stop_machine: simplify

On Tuesday 08 July 2008 21:44:40 Akinobu Mita wrote:
> I found a small possible cleanup in this patch.

Well spotted!  I think this cleanup is actually orthogonal to my patch,
so best served as a separate patch, how's this?

===
Hotplug CPU: don't check cpu_online after take_cpu_down

Akinobu points out that if take_cpu_down() succeeds, the cpu must be offline
(otherwise we're in deep trouble anyway.

Remove the cpu_online() check, and put a BUG_ON().

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Cc: "Akinobu Mita" <akinobu.mita@...il.com>

diff -r 805a2e5e68dd kernel/cpu.c
--- a/kernel/cpu.c	Tue Jul 08 23:04:48 2008 +1000
+++ b/kernel/cpu.c	Tue Jul 08 23:07:43 2008 +1000
@@ -226,8 +226,7 @@ static int __ref _cpu_down(unsigned int 
 	set_cpus_allowed_ptr(current, &tmp);
 
 	err = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
-
-	if (err || cpu_online(cpu)) {
+	if (err) {
 		/* CPU didn't die: tell everyone.  Can't complain. */
 		if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 					    hcpu) == NOTIFY_BAD)
@@ -235,6 +234,7 @@ static int __ref _cpu_down(unsigned int 
 
 		goto out_allowed;
 	}
+	BUG_ON(cpu_online(cpu));
 
 	/* Wait for it to sleep (leaving idle task). */
 	while (!idle_cpu(cpu))
--
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