[PATCH v2] watchdog: starfive-wdt: fix PM reference leak in probe error path

[Ivy Lopez <skunkolee@gmail.com>]

pm_runtime_resume_and_get() increments the runtime PM usage counter
and, via starfive_wdt_runtime_resume(), enables the clocks. If a
later step in probe() fails (reset_init, clock rate check,
watchdog_start, or watchdog_register_device), control reaches
err_exit, which calls pm_runtime_disable() but never balances the
earlier get, leaking the PM usage count.

Track whether a PM reference is currently held (pm_ref_held) and
whether the clocks are currently enabled (clocks_on), and use them
in err_exit to release exactly what was acquired:

 - if a PM reference is held, put it via pm_runtime_put_sync();
   only fall back to a manual clock disable if the resulting
   suspend transition did not actually run (put failure), since
   the runtime_suspend callback already disables the clocks on a
   successful put and a redundant call would double-disable them
   and underflow the clock enable count.
 - if no PM reference is held but the clocks were enabled directly
   (runtime PM disabled case), disable them manually.

Also propagate this accounting to the existing pm_runtime_put_sync()
call at the end of a successful probe: its usage-count decrement
happens regardless of the call's return value, so pm_ref_held must
be cleared immediately after calling it to avoid a second,
unbalanced put_sync() call if a later step in that path fails and
falls through to err_exit.

Fixes: db728ea9c7be ("drivers: watchdog: Add StarFive Watchdog driver")
Signed-off-by: Ivy Lopez <skunkolee@gmail.com>
---
v2:
 - Fix double clock-disable / clock-enable-count underflow when a
   PM reference was already released via a successful
   pm_runtime_put_sync() in err_exit
 - Fix double pm_runtime_put_sync() / usage-count underflow when
   falling through from the tail put failure to err_unregister_wdt

 drivers/watchdog/starfive-wdt.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/starfive-wdt.c b/drivers/watchdog/starfive-wdt.c
index af55adc4a3c6..4ad587732bda 100644
--- a/drivers/watchdog/starfive-wdt.c
+++ b/drivers/watchdog/starfive-wdt.c
@@ -429,6 +429,8 @@ static int starfive_wdt_probe(struct platform_device *pdev)
 {
 	struct starfive_wdt *wdt;
 	int ret;
+	bool pm_ref_held = false;
+	bool clocks_on = false;
 
 	wdt = devm_kzalloc(&pdev->dev, sizeof(*wdt), GFP_KERNEL);
 	if (!wdt)
@@ -449,11 +451,14 @@ static int starfive_wdt_probe(struct platform_device *pdev)
 		ret = pm_runtime_resume_and_get(&pdev->dev);
 		if (ret < 0)
 			return ret;
+		pm_ref_held = true;
+		clocks_on = true;
 	} else {
 		/* runtime PM is disabled but clocks need to be enabled */
 		ret = starfive_wdt_enable_clock(wdt);
 		if (ret)
 			return ret;
+		clocks_on = true;
 	}
 
 	ret = starfive_wdt_reset_init(&pdev->dev);
@@ -499,6 +504,9 @@ static int starfive_wdt_probe(struct platform_device *pdev)
 	if (!early_enable) {
 		if (pm_runtime_enabled(&pdev->dev)) {
 			ret = pm_runtime_put_sync(&pdev->dev);
+			pm_ref_held = false;
+			if (ret == 0)
+				clocks_on = false;
 			if (ret)
 				goto err_unregister_wdt;
 		}
@@ -509,7 +517,12 @@ static int starfive_wdt_probe(struct platform_device *pdev)
 err_unregister_wdt:
 	watchdog_unregister_device(&wdt->wdd);
 err_exit:
-	starfive_wdt_disable_clock(wdt);
+	if (pm_ref_held) {
+		if (pm_runtime_put_sync(&pdev->dev))
+			starfive_wdt_disable_clock(wdt);
+	} else if (clocks_on) {
+		starfive_wdt_disable_clock(wdt);
+	}
 	pm_runtime_disable(&pdev->dev);
 
 	return ret;
-- 
2.55.0