linux-kernel - [PATCH] x86/MCE/AMD: Fix thinko about thresholding

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Date:   Sat, 19 Nov 2016 11:34:02 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yazen Ghannam <Yazen.Ghannam@....com>
Subject: [PATCH] x86/MCE/AMD: Fix thinko about thresholding_en

From: Borislav Petkov <bp@...e.de>

So adding thresholding_en et al was a good thing for removing the
per-CPU thresholding callback, i.e., threshold_cpu_callback.

But, in order for it to work and especially that test in
mce_threshold_create_device() so that all thresholding banks get
properly created and not the whole thing to fail with a NULL ptr
dereference at mce_cpu_pre_down() when we offline the CPUs, we need to
set the thresholding_en flag *before* we start creating the devices.

Yap, it failed because thresholding_en wasn't set at the time
we were creating the banks so we didn't create any and then at
mce_cpu_pre_down() -> mce_threshold_remove_device() time, we would blow
up.

And the fix is actually easy: we have thresholding on the system when we
have managed to set the thresholding vector to amd_threshold_interrupt()
earlier in mce_amd_feature_init() while we were picking apart the
thresholding banks and what is set and what not.

So let's do that.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Yazen Ghannam <Yazen.Ghannam@....com>
Fixes: 4d7b02d58c40 ("x86/mcheck: Split threshold_cpu_callback into two callbacks")
---
 arch/x86/kernel/cpu/mcheck/mce_amd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce_amd.c b/arch/x86/kernel/cpu/mcheck/mce_amd.c
index 5c181610af58..bffc4253008b 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_amd.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_amd.c
@@ -1160,6 +1160,9 @@ static __init int threshold_init_device(void)
 {
 	unsigned lcpu = 0;

+	if (mce_threshold_vector == amd_threshold_interrupt)
+		thresholding_en = true;
+
 	/* to hit CPUs online before the notifier is up */
 	for_each_online_cpu(lcpu) {
 		int err = mce_threshold_create_device(lcpu);
@@ -1168,8 +1171,6 @@ static __init int threshold_init_device(void)
 			return err;
 	}

-	thresholding_en = true;
-
 	return 0;
 }
 /*
-- 
2.10.0