Hi Tomi, Thanks for your report. I have an on-going series trying to clean this all up [1]. The one change in the v4l-async core I proposed was however rejected and I have yet to circle back to figure out a different solution. Could you give it a try and see if it also solves this issue? 1. [PATCH 0/6] media: rcar-vin: Make use of multiple connections in v4l-async https://lore.kernel.org/linux-renesas-soc/20240129202254.1126012-1-niklas.soderlund+renesas@xxxxxxxxxxxx/ On 2024-09-06 12:57:50 +0300, Tomi Valkeinen wrote: > Hi Niklas, > > There seems to be a race in rcar-v4l2.c, causing > WARN_ON(entity->use_count < 0) in pipeline_pm_power_one(). > > If my understanding is correct, the VIN v4l2 nodes are being created > (rvin_v4l2_register), meaning they are userspace accessible, but the media > pipeline as a whole is not ready yet (e.g. media links). > > So what happens is that after some video nodes have been created, the > userspace opens them (I think it's udevd checking the new device nodes), > causing rvin_open(). rvin_open() goes through the media graph and does some > PM enabling (I'm not familiar with the legacy v4l2_pipeline_pm_get()). > However, as the links are not there, it doesn't really enable much at all. > > Then the driver goes forward and finishes with the media graph. > > Then the userspace closes the opened video nodes, rvin_release() gets called > and it goes through the media graph, which now contains all the entities, > and powers them down. As the entities were never powered up, we hit the > use_count warning. > > This happens quite often to me when loading the modules, but I think it can > be made to happen more often by adding msleep(1000) to the beginning of > rvin_release(), thus ensuring that the graph setup is finished before the > rvin_release() proceeds (and hoping that the graph setup was not ready when > rvin_open() was called). > > Tomi > -- Kind Regards, Niklas Söderlund
