[PATCH] hwrng: atmel: fix usage_count leak when autosuspend_delay is negative

[PATCH] hwrng: atmel: fix usage_count leak when autosuspend_delay is negative

[Guangshuo Li]

atmel_trng_probe() calls pm_runtime_use_autosuspend(), but neither the
probe failure path nor atmel_trng_remove() calls the matching
pm_runtime_dont_use_autosuspend() before disabling runtime PM.

If the autosuspend delay is set to a negative value while autosuspend
is enabled, the runtime PM core increments usage_count to prevent
runtime suspend. Without calling pm_runtime_dont_use_autosuspend()
during teardown, this reference is not dropped and usage_count remains
unbalanced.

Add the missing pm_runtime_dont_use_autosuspend() calls to both the
probe failure and remove paths before disabling runtime PM.

This issue was found by manual code inspection.

Fixes: c4f51eab6ce0 ("hwrng: atmel - add runtime pm support")
Cc: stable@vger.kernel.org
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
 drivers/char/hw_random/atmel-rng.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/char/hw_random/atmel-rng.c b/drivers/char/hw_random/atmel-rng.c
index 4ebbc44fecf0..6265d9a8d140 100644
--- a/drivers/char/hw_random/atmel-rng.c
+++ b/drivers/char/hw_random/atmel-rng.c
@@ -150,6 +150,7 @@ static int atmel_trng_probe(struct platform_device *pdev)
 
 	ret = devm_hwrng_register(&pdev->dev, &trng->rng);
 	if (ret) {
+		pm_runtime_dont_use_autosuspend(&pdev->dev);
 		pm_runtime_disable(&pdev->dev);
 		pm_runtime_set_suspended(&pdev->dev);
 #ifndef CONFIG_PM
@@ -165,6 +166,7 @@ static void atmel_trng_remove(struct platform_device *pdev)
 	struct atmel_trng *trng = platform_get_drvdata(pdev);
 
 	atmel_trng_cleanup(trng);
+	pm_runtime_dont_use_autosuspend(&pdev->dev);
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_set_suspended(&pdev->dev);
 }
-- 
2.43.0

Re: [PATCH] hwrng: atmel: fix usage_count leak when autosuspend_delay is negative

[Johan Hovold]

On Sat, Aug 08, 2026 at 02:34:58PM +0800, Guangshuo Li wrote:
> atmel_trng_probe() calls pm_runtime_use_autosuspend(), but neither the
> probe failure path nor atmel_trng_remove() calls the matching
> pm_runtime_dont_use_autosuspend() before disabling runtime PM.
> 
> If the autosuspend delay is set to a negative value while autosuspend
> is enabled, the runtime PM core increments usage_count to prevent
> runtime suspend. Without calling pm_runtime_dont_use_autosuspend()
> during teardown, this reference is not dropped and usage_count remains
> unbalanced.

As I've explained elsewhere, this is just misleading. There is no usage
count leak here as the count is balanced whenever the user re-enables
autosuspend through sysfs (by writing a non-negative timeout).

Drivers should clean up after themselves and disable autosuspend, but
this is more of a clean up than a fix and should not be backported.

You've sent upwards of 60 of these in the matter of a just a few days,
some which have even been picked up. Please send follow-ups (replies or
v2s) as soon as possible to prevent further of these from getting
merged.

> Add the missing pm_runtime_dont_use_autosuspend() calls to both the
> probe failure and remove paths before disabling runtime PM.
> 
> This issue was found by manual code inspection.
> 
> Fixes: c4f51eab6ce0 ("hwrng: atmel - add runtime pm support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>

Johan