pinctrl: avoid reload of p state in list iteration

When in the list_for_each_entry iteration, reload of p->state->settings
with a local setting from old_state will turn the list iteration into an
infinite loop.

The typical symptom when the issue happens, will be a printk message like:

  "not freeing pin xx (xxx) as part of deactivating group xxx - it is
already used for some other setting".

This is a compiler-dependent problem, one instance occurred using Clang
version 10.0 on the arm64 architecture with linux version 4.19.

Fixes: 6e5e959 ("pinctrl: API changes to support multiple states per device")
Signed-off-by: Maria Yu <quic_aiquny@quicinc.com>
Cc:  <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20231115102824.23727-1-quic_aiquny@quicinc.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Author: Maria Yu

drivers/pinctrl/core.c

@@ -1262,17 +1262,17 @@ static void pinctrl_link_add(struct pinctrl_dev *pctldev,
 static int pinctrl_commit_state(struct pinctrl *p, struct pinctrl_state *state)
 {
 	struct pinctrl_setting *setting, *setting2;
-	struct pinctrl_state *old_state = p->state;
+	struct pinctrl_state *old_state = READ_ONCE(p->state);
 	int ret;
 
-	if (p->state) {
+	if (old_state) {
 		/*
 		 * For each pinmux setting in the old state, forget SW's record
 		 * of mux owner for that pingroup. Any pingroups which are
 		 * still owned by the new state will be re-acquired by the call
 		 * to pinmux_enable_setting() in the loop below.
 		 */
-		list_for_each_entry(setting, &p->state->settings, node) {
+		list_for_each_entry(setting, &old_state->settings, node) {
 			if (setting->type != PIN_MAP_TYPE_MUX_GROUP)
 				continue;
 			pinmux_disable_setting(setting);