[PATCH] platform/x86: thinkpad_acpi: fix deadlock in hotkey input open/close

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

Commit d6479c25ecef ("platform/x86: thinkpad_acpi: Use
input_device_enabled()") changed hotkey_poll_setup() to acquire
tpacpi_inputdev->mutex and call input_device_enabled(tpacpi_inputdev).

However, the input core already holds dev->mutex when invoking a
device's open() and close() callbacks. Because hotkey_inputdev_open()
and hotkey_inputdev_close() call into hotkey_poll_setup(), attempting to
acquire tpacpi_inputdev->mutex again results in an immediate
self-deadlock.

Additionally, locking tpacpi_inputdev->mutex inside hotkey_poll_setup()
while holding hotkey_mutex introduces an ABBA lock ordering inversion
with hotkey_inputdev_open() and hotkey_inputdev_close(), which acquire
hotkey_mutex while holding tpacpi_inputdev->mutex. Finally,
input_inhibit_device() calls dev->close() before setting dev->inhibited,
so input_device_enabled() still returns true inside
hotkey_inputdev_close().

Track whether the input device is active in a driver-local boolean
protected by hotkey_mutex instead of locking tpacpi_inputdev->mutex and
querying input_device_enabled().

Fixes: d6479c25ecef ("platform/x86: thinkpad_acpi: Use input_device_enabled()")
Reported-by: Ali Ahmet Memiş <aliamemis@disroot.org>
Closes: https://lore.kernel.org/all/20260930075829.53484-1-aliamemis@disroot.org/
Reported-by: Qiling Zhu <kmatzkaczor244@gmail.com>
Closes: https://lore.kernel.org/all/asDVVtAXt8YVbZ3C@ThinkPad/
Reported-by: Oleksii Kryvenko <diver.ua@gmail.com>
Closes: https://lore.kernel.org/all/20261010002413.30007-1-krivenko@itstep.org/
Tested-by: Ali Ahmet Memiş <aliamemis@disroot.org>
Assisted-by: LLM
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/platform/x86/lenovo/thinkpad_acpi.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/platform/x86/lenovo/thinkpad_acpi.c b/drivers/platform/x86/lenovo/thinkpad_acpi.c
index 1225b01ed14d..40e9763a12f8 100644
--- a/drivers/platform/x86/lenovo/thinkpad_acpi.c
+++ b/drivers/platform/x86/lenovo/thinkpad_acpi.c
@@ -1887,6 +1887,7 @@ static u32 hotkey_reserved_mask;	/* events better left disabled */
 static u32 hotkey_driver_mask;		/* events needed by the driver */
 static u32 hotkey_user_mask;		/* events visible to userspace */
 static u32 hotkey_acpi_mask;		/* events enabled in firmware */
+static bool hotkey_input_enabled;
 
 static bool tpacpi_driver_event(const unsigned int hkey_event);
 static void hotkey_poll_setup(const bool may_warn);
@@ -2544,10 +2545,8 @@ static void hotkey_poll_setup(const bool may_warn)
 
 	lockdep_assert_held(&hotkey_mutex);
 
-	guard(mutex)(&tpacpi_inputdev->mutex);
 	if (hotkey_poll_freq > 0 &&
-	    (poll_driver_mask ||
-	     (poll_user_mask && input_device_enabled(tpacpi_inputdev)))) {
+	    (poll_driver_mask || (poll_user_mask && hotkey_input_enabled))) {
 		if (!tpacpi_hotkey_task) {
 			tpacpi_hotkey_task = kthread_run(hotkey_kthread,
 					NULL, TPACPI_NVRAM_KTHREAD_NAME);
@@ -2602,7 +2601,10 @@ static int hotkey_inputdev_open(struct input_dev *dev)
 	switch (tpacpi_lifecycle) {
 	case TPACPI_LIFE_INIT:
 	case TPACPI_LIFE_RUNNING:
-		hotkey_poll_setup_safe(false);
+		scoped_guard(mutex, &hotkey_mutex) {
+			hotkey_input_enabled = true;
+			hotkey_poll_setup(false);
+		}
 		return 0;
 	case TPACPI_LIFE_EXITING:
 		return -EBUSY;
@@ -2615,10 +2617,14 @@ static int hotkey_inputdev_open(struct input_dev *dev)
 
 static void hotkey_inputdev_close(struct input_dev *dev)
 {
+	guard(mutex)(&hotkey_mutex);
+
+	hotkey_input_enabled = false;
+
 	/* disable hotkey polling when possible */
 	if (tpacpi_lifecycle != TPACPI_LIFE_EXITING &&
 	    !(hotkey_source_mask & hotkey_driver_mask))
-		hotkey_poll_setup_safe(false);
+		hotkey_poll_setup(false);
 }
 
 /* sysfs hotkey enable ------------------------------------------------- */
-- 
2.56.0.385.gd3acb90ef8-goog