[PATCH 6/7] Input: gscps2 - serialize concurrent interrupt handlers

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

gscps2_interrupt() may be invoked concurrently from a hardware interrupt
on one CPU and from process context via gscps2_writeb_output() on another
CPU. In gscps2_report_data(), ps2port->lock is released before calling
serio_interrupt() to avoid recursive deadlocks. However, if two execution
contexts run gscps2_report_data() concurrently for the same port, they
could race to acquire serio->lock inside serio_interrupt(), potentially
delivering multi-byte scancodes out of order.

Serialize execution of gscps2_interrupt() using gscps2_interrupt_lock
with ACQUIRE(spinlock_irqsave_try). Using spin_trylock prevents
overlapping executions and guarantees in-order packet delivery without
risking recursive deadlocks if an input driver synchronously sends a
command back via serio_write(). If the lock cannot be acquired, return
IRQ_NONE to preserve spurious interrupt detection on shared IRQ lines.

Reported-by: sashiko-bot@kernel.org
Assisted-by: LLM
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/serio/gscps2.c | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/drivers/input/serio/gscps2.c b/drivers/input/serio/gscps2.c
index 907fb1537595..2afd53a163ff 100644
--- a/drivers/input/serio/gscps2.c
+++ b/drivers/input/serio/gscps2.c
@@ -288,6 +288,8 @@ static bool gscps2_report_data(struct gscps2port *ps2port)
 	}
 }
 
+static DEFINE_SPINLOCK(gscps2_interrupt_lock);
+
 /**
  * gscps2_interrupt() - Interruption service routine
  * @irq: interrupt number which triggered (unused)
@@ -305,21 +307,31 @@ static irqreturn_t gscps2_interrupt(int irq, void *dev)
 {
 	struct gscps2port *ps2port;
 	bool handled = false;
+	bool more_data;
+
+	ACQUIRE(spinlock_irqsave_try, lock)(&gscps2_interrupt_lock);
+	if (ACQUIRE_ERR(spinlock_irqsave_try, &lock))
+		return IRQ_NONE;
 
 	guard(rcu)();
 
-	list_for_each_entry_rcu(ps2port, &ps2port_list, node) {
-		if (gscps2_read_data(ps2port))
-			handled = true;
-	}
+	do {
+		more_data = false;
 
-	/* all data was read from the ports - now report the data to upper layer */
-	list_for_each_entry_rcu(ps2port, &ps2port_list, node) {
-		if (gscps2_report_data(ps2port)) {
-			/* More data ready - break early to restart interrupt */
-			break;
+		list_for_each_entry_rcu(ps2port, &ps2port_list, node) {
+			if (gscps2_read_data(ps2port))
+				handled = true;
 		}
-	}
+
+		/* all data was read from the ports - now report the data to upper layer */
+		list_for_each_entry_rcu(ps2port, &ps2port_list, node) {
+			if (gscps2_report_data(ps2port)) {
+				/* More data ready - restart loop to read new data */
+				more_data = true;
+				break;
+			}
+		}
+	} while (more_data);
 
 	return IRQ_RETVAL(handled);
 }

-- 
2.55.0.897.gb25b4bd76c-goog