linux-kernel - [PATCH 4/7] x86/mce: Avoid potential deadlock due to printk() in MCE context

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Date:	Thu, 16 Jul 2015 09:44:18 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Tony Luck <tony.luck@...el.com>, X86-ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, ashok.raj@...el.com,
	gong.chen@...ux.intel.com, Borislav Petkov <bp@...e.de>
Subject: [PATCH 4/7] x86/mce: Avoid potential deadlock due to printk() in MCE context

From: "Chen, Gong" <gong.chen@...ux.intel.com>

Printing in MCE context is a no-no, currently, as printk is not
NMI-safe. If some of the notifiers on the MCE chain call do so, we may
deadlock. In order to avoid that, delay printk() to process context
where it is safe to do so.

[Tony: Folded in subsequent patch from Boris for early boot logging]

Reported-by: Xie XiuQi <xiexiuqi@...wei.com>
Signed-off-by: Chen, Gong <gong.chen@...ux.intel.com>
Link: http://lkml.kernel.org/r/1432150538-3120-5-git-send-email-gong.chen@linux.intel.com
[ Boris: kick irq_work in mce_log() directly. ]
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 arch/x86/kernel/cpu/mcheck/mce-apei.c  | 1 -
 arch/x86/kernel/cpu/mcheck/mce.c       | 4 ++--
 arch/x86/kernel/cpu/mcheck/mce_intel.c | 1 -
 3 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce-apei.c b/arch/x86/kernel/cpu/mcheck/mce-apei.c
index a1aef9533154..34c89a3e8260 100644
--- a/arch/x86/kernel/cpu/mcheck/mce-apei.c
+++ b/arch/x86/kernel/cpu/mcheck/mce-apei.c
@@ -57,7 +57,6 @@ void apei_mce_report_mem_error(int severity, struct cper_sec_mem_err *mem_err)
 
 	m.addr = mem_err->physical_addr;
 	mce_log(&m);
-	mce_notify_irq();
 }
 EXPORT_SYMBOL_GPL(apei_mce_report_mem_error);
 
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index a76d3251cadf..b5214fc58920 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -159,7 +159,8 @@ void mce_log(struct mce *mce)
 	/* Emit the trace record: */
 	trace_mce_record(mce);
 
-	atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce);
+	if (mce_genpool_add(mce))
+		irq_work_queue(&mce_irq_work);
 
 	mce->finished = 0;
 	wmb();
@@ -1122,7 +1123,6 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 		/* assuming valid severity level != 0 */
 		m.severity = severity;
 		m.usable_addr = mce_usable_address(&m);
-		mce_genpool_add(&m);
 
 		mce_log(&m);
 
diff --git a/arch/x86/kernel/cpu/mcheck/mce_intel.c b/arch/x86/kernel/cpu/mcheck/mce_intel.c
index 844f56c5616d..70f567f774ed 100644
--- a/arch/x86/kernel/cpu/mcheck/mce_intel.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_intel.c
@@ -246,7 +246,6 @@ static void intel_threshold_interrupt(void)
 		return;
 
 	machine_check_poll(MCP_TIMESTAMP, this_cpu_ptr(&mce_banks_owned));
-	mce_notify_irq();
 }
 
 /*
-- 
1.9.0.258.g00eda23

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