[RFC PATCH 5/5] GHES: Make NMI handler have a single reader

Borislav Petkov
2015-03-27T09:22:58Z

From: Jiri Kosina <jkosina@suse.cz>

Since GHES sources are global, we theoretically need only a single CPU
reading them per NMI instead of a thundering herd of CPUs waiting on a
spinlock in NMI context for no reason at all.

Do that.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
drivers/acpi/apei/ghes.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 94a44bad5576..2bfd53cbfe80 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -729,10 +729,10 @@ static struct llist_head ghes_estatus_llist;
static struct irq_work ghes_proc_irq_work;

/*
- * NMI may be triggered on any CPU, so ghes_nmi_lock is used for
- * mutual exclusion.
+ * NMI may be triggered on any CPU, so ghes_in_nmi is used for
+ * having only one concurrent reader.
*/
-static DEFINE_RAW_SPINLOCK(ghes_nmi_lock);
+static atomic_t ghes_in_nmi = ATOMIC_INIT(0);

static LIST_HEAD(ghes_nmi);

@@ -840,7 +840,9 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
struct ghes *ghes;
int sev, ret = NMI_DONE;

- raw_spin_lock(&ghes_nmi_lock);
+ if (!atomic_add_unless(&ghes_in_nmi, 1, 1))
+ return ret;
+
list_for_each_entry_rcu(ghes, &ghes_nmi, list) {
if (ghes_read_estatus(ghes, 1)) {
ghes_clear_estatus(ghes);
@@ -863,7 +865,7 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
#ifdef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
irq_work_queue(&ghes_proc_irq_work);
#endif
- raw_spin_unlock(&ghes_nmi_lock);
+ atomic_dec(&ghes_in_nmi);
return ret;
}

--
2.3.3