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

[Jie Gan]

On 12/15/2025 5:51 PM, Leo Yan wrote:
> 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@xxxxxxxxxxxxxxx
> > > Fixes: 0e6c20517596 ("coresight: etm-perf: Allow an event to use different sinks")
> > > Signed-off-by: Ma Ke <make24@xxxxxxxxxxx>
> > > ---
> > > 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.

That make sense. We dont need to hold the refcnt for a while and it 
should be released immediately after locating the required device.

Thanks,
Jie

> > 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