On 02/02/2017 02:35 PM, Russell King - ARM Linux wrote:
<snip> However, "*vfd" contains a struct device, and you _correctly_ set the release function for "*vfd" to video_device_release via camif_videodev. However, if you try to rmmod imx-media, then you end up with a kernel warning that you're freeing memory containing a held lock, and later chaos ensues because kmalloc has been corrupted. The root cause of this is embedding the device structure within the video_device into the driver's private data. *Any* structure what so ever that contains a kref is reference counted, and that includes struct device, and therefore also includes struct video_device. What that means is that its lifetime is _not_ under _your_ control, and you may not free it except through its release function (which is video_device_release().) However, that also tries to kfree (with an offset of 4) your private data, which results in the warning and the corrupted kmalloc free lists. The solution is simple, make "vfd" a pointer in your private data structure and kmalloc() it separately, letting video_device_release() kfree() that data when it needs to.
Thanks Russell for tracking this down. I remember doing this when I was reviewing the code for opportunities to "optimize" :-/, and carelessly caused this bug by not reviewing how video_device is freed. Fixed. Steve -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
