Re: [PATCH V7 02/24] coresight: associating path with session rather than tracer

From: Rabin Vincent
Date: Sun Jan 10 2016 - 10:43:35 EST

On Tue, Jan 05, 2016 at 03:23:20PM -0700, Mathieu Poirier wrote:
> On 5 January 2016 at 06:15, Rabin Vincent <rabin@xxxxxx> wrote:
> > The command sequence is exactly as mentioned above. The kernel is
> > v4.4rc-8 + all your patches from this thread + the OMAP coresight patch
> > I mentioned earlier.
> What patch was that? Would mind providing me with more information?

> I fixed the kmalloc bug - it stemmed from a rebase conflict in the
> etm3x driver. On the flip side I haven't been able to reproduce the
> lockdep problem. But looking at the log you provided I can understand
> why the kernel is complaining.
> I produced a patch [1] and added you as a reporter. It would be great
> if you could give it a quick spin to see if the problem still persist.
> [1].

It does silence the warning but simply using mutex_trylock() instead of
mutex_lock() does not seem like the correct fix. The lock dependency
problem lockdep is complaining about can be fixed for example by not
holding the coresight_mutex around the device_unregister()
coresight_unregister(). I don't quite see what the mutex is protecting

BTW, there seem to be several problems with the unregistration:

- csdev->refcnt which is allocated with kcalloc() in
coresight_register() is never freed.

- csdev->conns is freed before device_unregister() rather than in the
release function.

- put_device() is not done on the csdev' conn->child_devs when it is
unregistered, so the reference taken by the bus_find_device() in
coresight_fixup_device_conns() is never released.

- There is no reference taken for the csdev when it is assigned as
some other device's child_dev in coresight_orphan_match()