linux-kernel - Re: [PULL] x86 cpumask work

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Message-Id: <200903151326.34114.rusty@rustcorp.com.au>
Date:	Sun, 15 Mar 2009 13:26:33 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Mike Travis <travis@....com>
Subject: Re: [PULL] x86 cpumask work

On Saturday 14 March 2009 01:57:42 Ingo Molnar wrote:
> Note, it might have crashed in a cpu hotplug test i'm conducting 
> during bootup:
> 
> echo 0 > /sys/devices/system/cpu/cpu1/online

Indeed, thanks!

Subject: cpumask: fix crash when offlining cpus

Impact: Fix cpu offline when CONFIG_MAXSMP=y

Changeset bc9b83dd1f66402b870301c3c7117b9c1484abb4 "cpumask: convert c1e_mask
in arch/x86/kernel/process.c to cpumask_var_t" contained a bug: c1e_mask is
manipulated even if C1E isn't detected (and hence not allocated).  This is
simply fixed by checking for NULL (which gcc optimizes out anyway of
CONFIG_CPUMASK_OFFSTACK=n, since it knows ce1_mask can never be NULL).

In addition, fix a leak where select_idle_routine re-allocates (and re-clears)
c1e_mask on every cpu init.

Reported-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index cad5431..91a8c26 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -479,7 +479,8 @@ static int c1e_detected;
 
 void c1e_remove_cpu(int cpu)
 {
-	cpumask_clear_cpu(cpu, c1e_mask);
+	if (c1e_mask != NULL)
+		cpumask_clear_cpu(cpu, c1e_mask);
 }
 
 /*
@@ -556,8 +557,11 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 		pm_idle = mwait_idle;
 	} else if (check_c1e_idle(c)) {
 		printk(KERN_INFO "using C1E aware idle routine\n");
-		alloc_cpumask_var(&c1e_mask, GFP_KERNEL);
-		cpumask_clear(c1e_mask);
+		/* c1e_mask can only be NULL during boot of first cpu. */
+		if (c1e_mask == NULL) {
+			alloc_cpumask_var(&c1e_mask, GFP_KERNEL);
+			cpumask_clear(c1e_mask);
+		}
 		pm_idle = c1e_idle;
 	} else
 		pm_idle = default_idle;
--
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