[RFC PATCH v4 09/21] x86/nmi: Add a NMI_WATCHDOG NMI handler category

[Ricardo Neri]

Add a NMI_WATCHDOG as a new category of NMI handler. This new category
is to be used with the HPET-based hardlockup detector. This detector
does not have a direct way of checking if the HPET timer is the source of
the NMI. Instead it indirectly estimate it using the time-stamp counter.

Therefore, we may have false-positives in case another NMI occurs within
the estimated time window. For this reason, we want the handler of the
detector to be called after all the NMI_LOCAL handlers. A simple way
of achieving this with a new NMI handler category.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/nmi.h |  1 +
 arch/x86/kernel/nmi.c      | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index 75ded1d13d98..75aa98313cde 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -29,6 +29,7 @@ enum {
 	NMI_UNKNOWN,
 	NMI_SERR,
 	NMI_IO_CHECK,
+	NMI_WATCHDOG,
 	NMI_MAX
 };
 
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 4df7705022b9..43e96aedc6fe 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -64,6 +64,10 @@ static struct nmi_desc nmi_desc[NMI_MAX] =
 		.lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[3].lock),
 		.head = LIST_HEAD_INIT(nmi_desc[3].head),
 	},
+	{
+		.lock = __RAW_SPIN_LOCK_UNLOCKED(&nmi_desc[4].lock),
+		.head = LIST_HEAD_INIT(nmi_desc[4].head),
+	},
 
 };
 
@@ -174,6 +178,8 @@ int __register_nmi_handler(unsigned int type, struct nmiaction *action)
 	 */
 	WARN_ON_ONCE(type == NMI_SERR && !list_empty(&desc->head));
 	WARN_ON_ONCE(type == NMI_IO_CHECK && !list_empty(&desc->head));
+	WARN_ON_ONCE(type == NMI_WATCHDOG && !list_empty(&desc->head));
+
 
 	/*
 	 * some handlers need to be executed first otherwise a fake
@@ -384,6 +390,10 @@ static void default_do_nmi(struct pt_regs *regs)
 	}
 	raw_spin_unlock(&nmi_reason_lock);
 
+	handled = nmi_handle(NMI_WATCHDOG, regs);
+	if (handled == NMI_HANDLED)
+		return;
+
 	/*
 	 * Only one NMI can be latched at a time.  To handle
 	 * this we may process multiple nmi handlers at once to
-- 
2.17.1