Hi Maxime, On Thu, 10 Jul 2025 09:27:09 +0200 Maxime Ripard <[email protected]> wrote:
> Hi, > > On Wed, Jul 09, 2025 at 06:48:07PM +0200, Luca Ceresoli wrote: > > The bridge returned by drm_bridge_get_next_bridge() is refcounted. Put it > > when done. > > > > Signed-off-by: Luca Ceresoli <[email protected]> > > You should really expand a bit more your commit logs, and provide the > context of why you think putting drm_bridge_put where you do is a good idea. > > > --- > > drivers/gpu/drm/drm_bridge.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > > index > > 0b450b334afd82e0460f18fdd248f79d0a2b153d..05e85457099ab1e0a23ea7842c9654c9a6881dfb > > 100644 > > --- a/drivers/gpu/drm/drm_bridge.c > > +++ b/drivers/gpu/drm/drm_bridge.c > > @@ -1147,6 +1147,8 @@ drm_atomic_bridge_propagate_bus_flags(struct > > drm_bridge *bridge, > > } else { > > next_bridge_state = drm_atomic_get_new_bridge_state(state, > > next_bridge); > > + drm_bridge_put(next_bridge); > > + > > /* > > * No bridge state attached to the next bridge, just leave the > > * flags to 0. > > In particular, I don't think it is here. > > You still have a variable in scope after that branch that you would have > given up the reference for, which is pretty dangerous. > > Also, the bridge state lifetime is shorter than the bridge lifetime > itself, so we probably want to have the drm_bridge_put after we're done > with next_bridge_state too. Totally agree about this. I theory moving the _put just after the last usage of next_bridge_state would be enough. However... > Overall, I think using __free here is probably the most robust solution. ...I'm OK with using use __free here, even though it doesn't look strictly necessary. However for patch 9 the code path is slightly more complex, so I'll use __free for both. With this change, this patch would become: @@ -1121,7 +1121,6 @@ drm_atomic_bridge_propagate_bus_flags(struct drm_bridge *bridge, struct drm_atomic_state *state) { struct drm_bridge_state *bridge_state, *next_bridge_state; - struct drm_bridge *next_bridge; u32 output_flags = 0; bridge_state = drm_atomic_get_new_bridge_state(state, bridge); @@ -1130,7 +1129,7 @@ drm_atomic_bridge_propagate_bus_flags(struct drm_bridge *bridge, if (!bridge_state) return; - next_bridge = drm_bridge_get_next_bridge(bridge); + struct drm_bridge *next_bridge __free(drm_bridge_put) = drm_bridge_get_next_bridge(bridge); /* * Let's try to apply the most common case here, that is, propagate And a tentative commit message body is: The bridge returned by drm_bridge_get_next_bridge() is refcounted. Put it when done. We need to ensure it is not put before either next_bridge or next_bridge_state is in use, thus for simplicity use a cleanup action. I'll resend with the above changes (unless you have more improvements to suggest) in a few days, to wait for any feedback on patch 1. Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
