[PATCH 3/4] soc: qcom: smp2p: Add memory barrier for irq_pending

[Chris Lew <quic_clew@quicinc.com>]

There is a very tight race where the irq_retrigger function is run
on one cpu and the actual retrigger softirq is running on a second
cpu. When this happens, there may be a chance that the second cpu
will not see the updated irq_pending value from first cpu.

Add a memory barrier to ensure that irq_pending is read correctly.

Signed-off-by: Chris Lew <quic_clew@quicinc.com>
---
 drivers/soc/qcom/smp2p.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/soc/qcom/smp2p.c b/drivers/soc/qcom/smp2p.c
index a94cddcb0298..a1ea5f55c228 100644
--- a/drivers/soc/qcom/smp2p.c
+++ b/drivers/soc/qcom/smp2p.c
@@ -249,6 +249,9 @@ static void qcom_smp2p_notify_in(struct qcom_smp2p *smp2p)
 
 		status = val ^ entry->last_value;
 		entry->last_value = val;
+
+		/* Ensure irq_pending is read correctly */
+		mb();
 		status |= *entry->irq_pending;
 
 		/* No changes of this entry? */
@@ -356,6 +359,11 @@ static int smp2p_retrigger_irq(struct irq_data *irqd)
 
 	set_bit(irq, entry->irq_pending);
 
+	/* Ensure irq_pending is visible to all cpus that retried interrupt
+	 * can run on
+	 */
+	mb();
+
 	return 0;
 }
 
-- 
2.7.4