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Date: Sun, 26 Jul 2015 10:41:54 +0200
From: Borislav Petkov <bp@alien8.de>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Philip =?utf-8?Q?M=C3=BCller?= <philm@manjaro.org>,
        linux-kernel@vger.kernel.org, Sudeep Holla <sudeep.holla@arm.com>,
        Guenter Roeck <linux@roeck-us.net>, manjaro-dev@manjaro.org,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Andre Przywara <andre.przywara@arm.com>, Borislav Petkov <bp@suse.de>
Subject: Re: [linux41] regression with 'x86/cacheinfo: Move cacheinfo sysfs
 code to generic infrastructure' on AMD i686
Message-ID: <20150726084154.GA14829@nazgul.tnic>
References: <55B16967.1040609@manjaro.org>
 <55B47BB8.6080202@manjaro.org>
 <alpine.DEB.2.11.1507261012480.18576@nanos>
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On Sun, Jul 26, 2015 at 10:13:45AM +0200, Thomas Gleixner wrote:
> On Sun, 26 Jul 2015, Philip Müller wrote:
> > > task: f58e0000 ti: f58e8000 task.ti: f58e800
> > > EIP: 0060:[<c135a903>] EFLAGS: 00010206 CPU: 0
> > > EIP is at free_cache_attributes+0x83/0xd0
> > > EAX: 00000001 EBX: f589d46c ECX: 00000090 EDX: 360c2000
> > > ESI: 00000000 EDI: c1724a80 EBP: f58e9ec0 ESP: f58e9ea0
> > >  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
> > > CR0: 8005003b CR2: 000000ac CR3: 01731000 CR4: 000006d0
> 
> That's a trivial NULL pointer dereference in the error/cleanup
> path. Patch below should fix it.

Well, I got a bit different, and of course totally untested possible
solution:

cache_shared_cpu_map_setup() does check sib_cpu_ci->info_list before
setting cpumask bits while cache_shared_cpu_map_remove() doesn't. Ballancing
this out would mean:

---
diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index 764280a91776..8a4546dc25e3 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -148,7 +148,11 @@ static void cache_shared_cpu_map_remove(unsigned int cpu)
 
 			if (sibling == cpu) /* skip itself */
 				continue;
+
 			sib_cpu_ci = get_cpu_cacheinfo(sibling);
+			if (!sib_cpu_ci->info_list)
+				continue;
+
 			sib_leaf = sib_cpu_ci->info_list + index;
 			cpumask_clear_cpu(cpu, &sib_leaf->shared_cpu_map);
 			cpumask_clear_cpu(sibling, &this_leaf->shared_cpu_map);
---

Now Philip can have some more fun testing :-)

-- 
Regards/Gruss,
    Boris.

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