linux-kernel - [PATCH 2/2] powerpc/book3s: mce: Use add_taint_no_warn() in machine_check

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Message-Id: <148765089349.20315.11180051017586952500.stgit@jupiter.in.ibm.com>
Date:   Tue, 21 Feb 2017 09:51:33 +0530
From:   Mahesh J Salgaonkar <mahesh@...ux.vnet.ibm.com>
To:     linuxppc-dev <linuxppc-dev@...abs.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 2/2] powerpc/book3s: mce: Use add_taint_no_warn() in
 machine_check_early().

From: Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>

machine_check_early() gets called in real mode. The very first time when
add_taint() is called, it prints a warning which ends up calling opal
call (that uses OPAL_CALL wrapper) for writing it to console. If we get a
very first machine check while we are in opal we are doomed. OPAL_CALL
overwrites the PACASAVEDMSR in r13 and in this case when we are done with
MCE handling the original opal call will use this new MSR on it's way
back to opal_return. This usually leads unexpected behaviour or kernel
to panic. Instead use the add_taint_no_warn() that does not call printk.

This is broken with current FW level. We got lucky so far for not getting
very first MCE hit while in OPAL. But easily reproducible on Mambo.
This should go to stable as well alongwith patch 1/2.

Fixes: 27ea2c420cad powerpc: Set the correct kernel taint on machine check errors.
Signed-off-by: Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/traps.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 62b587f..4a048dc 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -306,7 +306,7 @@ long machine_check_early(struct pt_regs *regs)

 	__this_cpu_inc(irq_stat.mce_exceptions);

-	add_taint(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);
+	add_taint_no_warn(TAINT_MACHINE_CHECK, LOCKDEP_NOW_UNRELIABLE);

 	/*
 	 * See if platform is capable of handling machine check. (e.g. PowerNV