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
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