ACPI: PM: s2idle: Avoid possible race related to the EC GPE

It is theoretically possible for the ACPI EC GPE to be set after the
s2idle_ops->wake() called from s2idle_loop() has returned and before
the subsequent pm_wakeup_pending() check is carried out.  If that
happens, the resulting wakeup event will cause the system to resume
even though it may be a spurious one.

To avoid that race, first make the ->wake() callback in struct
platform_s2idle_ops return a bool value indicating whether or not
to let the system resume and rearrange s2idle_loop() to use that
value instad of the direct pm_wakeup_pending() call if ->wake() is
present.

Next, rework acpi_s2idle_wake() to process EC events and check
pm_wakeup_pending() before re-arming the SCI for system wakeup
to prevent it from triggering prematurely and add comments to
that function to explain the rationale for the new code flow.

Fixes: 56b991849009 ("PM: sleep: Simplify suspend-to-idle control flow")
Cc: 5.4+ <stable@vger.kernel.org> # 5.4+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 2c47280fbfc7..8b1bb5ee7e5d 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -131,11 +131,12 @@ static void s2idle_loop(void)
 	 * to avoid them upfront.
 	 */
 	for (;;) {
-		if (s2idle_ops && s2idle_ops->wake)
-			s2idle_ops->wake();
-
-		if (pm_wakeup_pending())
+		if (s2idle_ops && s2idle_ops->wake) {
+			if (s2idle_ops->wake())
+				break;
+		} else if (pm_wakeup_pending()) {
 			break;
+		}
 
 		pm_wakeup_clear(false);