From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay2-d.mail.gandi.net (relay2-d.mail.gandi.net [217.70.183.194]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8CBA21FBE87 for ; Mon, 14 Jul 2025 10:08:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.183.194 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752487738; cv=none; b=ZKkbGQaBTiIX9bK+SIxfWCFb+sKbxWE93fRqkT+2W5AOHFzAiNvAe2n0at7QZW43i/9dBCTybKCr8gxkFfRxO/P1erAB40aR9Vs7LYDBL8/8nRGa9q9KEjSamw1AMwThr9iMKbJsdeBrTGIPyzsk264jfNrEFEP2y2p2Q3GLG+o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752487738; c=relaxed/simple; bh=sUbfXG/kIveTshOzurB1Oe+PyDBe1n88waGVjM3wNbY=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=PXrvyttPAF6rozmznpejCAWKox/TYOEEkyxtHo2IBqDgToTJV6q8ZziudrmMPVPloKVxaChSGEEfuPNECSddBBi/TiSPO1ZHpcL5/vRQteoM08MPmv4ME2HEMrt405f8ihCNyXsRDSd+QeJoD2AaGYoJi1F4CU16fyTwPvyLWsY= ARC-Authentication-Results:i=1; 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bh=xgutdRjLLdQi2RnkqaGrlwK27BoBj8ki0FopHfGLe9A=; b=FndN3beY+pz3fPT55Ct9FIe1LlXQ/Q/0trzzGTE7v8shKaH6N8hB6rSUm5xc18XaWT6uXM WBa/3dW/YemVx5qHH4SV+U/urhVy7ebch00KZ+tby7S8Jz1aQKkhH1coLFGtqkFDqsTFnR IJBGe8FLiHYPZSFtmB/Zj4h0Mos6wc5s2K/U5FWZ/Af3yzyKzsXaHtz6v3j6EK6YY1/ECn +El+AYDpTXnPJ1wT1dWQPHgw1g6eRf+aod4AHiIhqPlbv3nQAkC9dSfImFuSsIrwO1JTvC Fyhg88E/VCE50CEOgXoHYDUA2Z8lLgF7W9haRc3nM0OMYJ8u/iK8d2o1dg+Npw== Date: Mon, 14 Jul 2025 12:08:42 +0200 From: Luca Ceresoli To: Maxime Ripard Cc: Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Maarten Lankhorst , Thomas Zimmermann , David Airlie , Simona Vetter , Liu Ying , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Tomi Valkeinen , Philipp Zabel , Hui Pu , Thomas Petazzoni , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 8/9] drm/bridge: put the bridge returned by drm_bridge_get_next_bridge() Message-ID: <20250714120842.3b336998@booty> In-Reply-To: <20250710-classic-bouncy-caiman-8e2045@houat> References: <20250709-drm-bridge-alloc-getput-drm_bridge_get_next_bridge-v1-0-48920b9cf369@bootlin.com> <20250709-drm-bridge-alloc-getput-drm_bridge_get_next_bridge-v1-8-48920b9cf369@bootlin.com> <20250710-classic-bouncy-caiman-8e2045@houat> Organization: Bootlin X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: imx@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-GND-State: clean X-GND-Score: -100 X-GND-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtdefgdehudeijecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfitefpfffkpdcuggftfghnshhusghstghrihgsvgenuceurghilhhouhhtmecufedtudenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhepfffhvfevuffkjghfohfogggtgfesthejredtredtvdenucfhrhhomhepnfhutggrucevvghrvghsohhlihcuoehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmqeenucggtffrrghtthgvrhhnpeeglefffefghefhtddvfeeufeeiveekgffgleekieduteekkeetvdehudekgfdvvdenucffohhmrghinhepsghoohhtlhhinhdrtghomhenucfkphepvdgrtddvmeeijedtmedvtddvtdemvggrtddumegsvgegudemleehvgejmeefgeefmeeludefvgenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepihhnvghtpedvrgdtvdemieejtdemvddtvddtmegvrgdtudemsggvgedumeelhegvjeemfeegfeemledufegvpdhhvghlohepsghoohhthidpmhgrihhlfhhrohhmpehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmpdhnsggprhgtphhtthhopedvgedprhgtphhtthhopehmrhhiphgrrhgusehkvghrnhgvlhdrohhrghdprhgtphhtthhopegrnhgurhiivghjrdhhrghjuggrsehinhhtvghlrdgtohhmpdhrtghpthhtohepnhgvihhlrdgrrhhmshhtrhhonhhgsehlihhnrghro hdrohhrghdprhgtphhtthhopehrfhhoshhssehkvghrnhgvlhdrohhrghdprhgtphhtthhopefnrghurhgvnhhtrdhpihhntghhrghrthesihguvggrshhonhgsohgrrhgurdgtohhmpdhrtghpthhtohepjhhonhgrsheskhifihgsohhordhsvgdprhgtphhtthhopehjvghrnhgvjhdrshhkrhgrsggvtgesghhmrghilhdrtghomhdprhgtphhtthhopehmrggrrhhtvghnrdhlrghnkhhhohhrshhtsehlihhnuhigrdhinhhtvghlrdgtohhm X-GND-Sasl: luca.ceresoli@bootlin.com Hi Maxime, On Thu, 10 Jul 2025 09:27:09 +0200 Maxime Ripard 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 > > 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