Re: [PATCH v2 RESEND] coresight: etm-perf: Fix reference count leak in etm_setup_aux

[Leo Yan <leo.yan@arm.com>]

On Mon, Dec 15, 2025 at 11:02:08AM +0200, James Clark wrote:
> 
> 
> On 15/12/2025 04:27, Ma Ke wrote:
> > In etm_setup_aux(), when a user sink is obtained via
> > coresight_get_sink_by_id(), it increments the reference count of the
> > sink device. However, if the sink is used in path building, the path
> > holds a reference, but the initial reference from
> > coresight_get_sink_by_id() is not released, causing a reference count
> > leak. We should release the initial reference after the path is built.
> > 
> > Found by code review.
> > 
> > Cc: stable@vger.kernel.org
> > Fixes: 0e6c20517596 ("coresight: etm-perf: Allow an event to use different sinks")
> > Signed-off-by: Ma Ke <make24@iscas.ac.cn>
> > ---
> > Changes in v2:
> > - modified the patch as suggestions.
> 
> I think Leo's comment on the previous v2 is still unaddressed. But releasing
> it in coresight_get_sink_by_id() would make it consistent with
> coresight_find_csdev_by_fwnode() and prevent further mistakes.

The point is the coresight core layer uses coresight_grab_device() to
increase the device's refcnt.  This is why we don't need to grab a
device when setup AUX.

> It also leads me to see that users of coresight_find_device_by_fwnode()
> should also release it, but only one out of two appears to.

Good finding!

Thanks,
Leo