Input: avoid calling input_set_abs_val() in the event handling core

input_abs_set_val() can nominally call input_alloc_absinfo() which may
allocate memory with GFP_KERNEL flag. This does not happen when
input_abs_set_val() is called by the input core to set current MT slot when
handling a new input event, but it trips certain static analyzers.

Rearrange the code to access the relevant structures directly.
Reported-by: Teng Qi <starmiku1207184332@gmail.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Link: https://lore.kernel.org/r/ZFBg379uuHjf+YEM@google.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/input.c

@@ -190,6 +190,7 @@ static int input_handle_abs_event(struct input_dev *dev,
 				  unsigned int code, int *pval)
 {
 	struct input_mt *mt = dev->mt;
+	bool is_new_slot = false;
 	bool is_mt_event;
 	int *pold;
 
@@ -210,6 +211,7 @@ static int input_handle_abs_event(struct input_dev *dev,
 		pold = &dev->absinfo[code].value;
 	} else if (mt) {
 		pold = &mt->slots[mt->slot].abs[code - ABS_MT_FIRST];
+		is_new_slot = mt->slot != dev->absinfo[ABS_MT_SLOT].value;
 	} else {
 		/*
 		 * Bypass filtering for multi-touch events when
@@ -228,8 +230,8 @@ static int input_handle_abs_event(struct input_dev *dev,
 	}
 
 	/* Flush pending "slot" event */
-	if (is_mt_event && mt && mt->slot != input_abs_get_val(dev, ABS_MT_SLOT)) {
-		input_abs_set_val(dev, ABS_MT_SLOT, mt->slot);
+	if (is_new_slot) {
+		dev->absinfo[ABS_MT_SLOT].value = mt->slot;
 		return INPUT_PASS_TO_HANDLERS | INPUT_SLOT;
 	}