Re: [PATCH] drm: bridge: cdns-mhdp8546: Fix PM reference leak in cdns_mhdp_probe()

From: yukuai (C)
Date: Sat May 29 2021 - 05:15:25 EST


ping ...

On 2021/05/18 20:58, Robert Foss wrote:
On Tue, 18 May 2021 at 09:42, Johan Hovold <johan@xxxxxxxxxx> wrote:

On Mon, May 17, 2021 at 11:27:38AM +0200, Robert Foss wrote:
Hey Yu,

On Mon, 17 May 2021 at 10:08, Yu Kuai <yukuai3@xxxxxxxxxx> wrote:

pm_runtime_get_sync will increment pm usage counter even it failed.
Forgetting to putting operation will result in reference leak here.
Fix it by replacing it with pm_runtime_resume_and_get to keep usage
counter balanced.

Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
index 0cd8f40fb690..305489d48c16 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
@@ -2478,7 +2478,7 @@ static int cdns_mhdp_probe(struct platform_device *pdev)
clk_prepare_enable(clk);

pm_runtime_enable(dev);
- ret = pm_runtime_get_sync(dev);
+ ret = pm_runtime_resume_and_get(dev);
if (ret < 0) {
dev_err(dev, "pm_runtime_get_sync failed\n");

This error message is a bit confusing now, could you update it.

pm_runtime_disable(dev);

The code is correct as it is. If pm_runtime_get_sync() fails and
increments[1] the pm.usage_count variable, that isn't a problem since
pm_runtime_disable() disables pm, and resets pm.usage_count variable
to zero[2].

No it doesn't; pm_runtime_disable() does not reset the counter and you
still need to decrement the usage count when pm_runtime_get_sync()
fails.

Thanks for chiming in Johan, you're absolutely right and I must have
misread something.

With the above fix, feel free to add my r-b.

Reviewed-by: Robert Foss <robert.foss@xxxxxxxxxx>
.