linux-kernel - Re: 2.6.34-rc2 - crash on shutdown

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Message-ID: <4BA8C7A4.8050502@ladisch.de>
Date:	Tue, 23 Mar 2010 14:52:36 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Stephane Eranian <eranian@...gle.com>
CC:	David R <david@...olicited.net>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.34-rc2 - crash on shutdown

Stephane Eranian wrote:
> On Tue, Mar 23, 2010 at 1:02 PM, Clemens Ladisch <clemens@...isch.de> wrote:
> > The only pointer access in this function is cpuhw->amd_nb, but
> > I don't see any obvious bugs.
> 
> I reported a problem with the AMD initialization just last week.
> There is an issue with amd_pmu_cpu_online() which gets called
> too early, and thus fails. That leaves some bogus state and causes
> a crash in amd_pmu_cpu_offline().
> 
> I proposed a fix which was rejected. The alternative involves moving
> some the of CPU initialization code (on AMD) to an earlier position,i.e.,
> which would be executed before the CPU_STARTED notifier. Nobody
> has proposed anything else so far.

I don't know about the early bootmem stuff, but regardless of this issue,
if amd_pmu_cpu_online() can fail, then amd_pmu_cpu_offline() must be able
to handle this without blowing up.  Something like this (untested):

Signed-off-by: Clemens Ladisch <clemens@...isch.de>

--- a/arch/x86/kernel/cpu/perf_event_amd.c
+++ b/arch/x86/kernel/cpu/perf_event_amd.c
@@ -324,17 +324,17 @@ static void amd_pmu_cpu_online(int cpu)
 	if (boot_cpu_data.x86_max_cores < 2)
 		return;
 
+	cpu1 = &per_cpu(cpu_hw_events, cpu);
+	cpu1->amd_nb = NULL;
+
 	/*
 	 * function may be called too early in the
 	 * boot process, in which case nb_id is bogus
 	 */
 	nb_id = amd_get_nb_id(cpu);
 	if (nb_id == BAD_APICID)
 		return;
 
-	cpu1 = &per_cpu(cpu_hw_events, cpu);
-	cpu1->amd_nb = NULL;
-
 	raw_spin_lock(&amd_nb_lock);
 
 	for_each_online_cpu(i) {
@@ -370,7 +370,7 @@ static void amd_pmu_cpu_offline(int cpu)
 
 	raw_spin_lock(&amd_nb_lock);
 
-	if (--cpuhw->amd_nb->refcnt == 0)
+	if (cpuhw->amd_nb && --cpuhw->amd_nb->refcnt == 0)
 		kfree(cpuhw->amd_nb);
 
 	cpuhw->amd_nb = NULL;
--
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