From nobody Thu Oct 9 04:18:58 2025 Received: from relay5-d.mail.gandi.net (relay5-d.mail.gandi.net [217.70.183.197]) (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 512B128313A for ; Fri, 20 Jun 2025 09:32:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.183.197 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750411959; cv=none; b=TVRyTTiO3IlW7Bhga5xHP7QsuufKe0uC991y09/Qj8uDj9v+Qm5JE2kDbaF/1OiDnjFue2dFZsnpD8sARWuIuj9Tgc9hGUcXeSMtoar1UVYOovTjUvPL/G4BJ8g4E+ztrobtnMFpjJ0vaOzmmsbV/WGrHGuUaR4uQRBi/RQb6cI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750411959; c=relaxed/simple; bh=iieGhevUOutzD2imOkHyTsbQZuGXWnuEOKLK9OSzie8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=D83Bca3JJQ8pM9BhpEegoxYCs6fmyjbhrCggwYCzlr2LXgQMpH/pcwS0ZyoLcZP0kXpakEF3It5yr5xC8SiIauTsoh/TKXtUN9xLc2xdAmWYA8AVAqGD7M3DRcSfoIgcfx9RioD/QjOs0eeJL2cU95JozbhauhEPOtqKPZBQ89A= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=kshl+dTn; arc=none smtp.client-ip=217.70.183.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="kshl+dTn" Received: by mail.gandi.net (Postfix) with ESMTPSA id 7905B41CFD; Fri, 20 Jun 2025 09:32:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1750411955; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Og/abJgrUqfxjsS4tOXPNFKEAFZRYJ9MNhUKQuNvNHY=; b=kshl+dTnu+cru5BATollAiVfbvs0owrC1lKuPCgQc4xd+grzHFwM92WovACoGTGfWKrbh0 d6iFxgGo50htxD+cLQnkSxKFopoOZBu50GfYCH5cErLDN8aW07DxWSXKMSTXpm8OzziGKh Z+Zo3m3yLAfYrddEtSFBxtFQ/A4EqVxGF++XCLKsM0pgSTH1k9SU69DUSjt6lGil/rrQrW vXdAjDJ06BgJH8Gtn5uxGvuwwLEz008HP2iXzSUE9K6UyI6GlmjfvavWViM/TazgtB7v7y RtMw5xMBgp/blBOxPvj2uod2HmLEcT0gbE31ipuMOD3/ulCNRFHi8Ffxyp8Myg== From: Luca Ceresoli Date: Fri, 20 Jun 2025 11:32:06 +0200 Subject: [PATCH 1/3] drm/bridge: get/put the bridge reference in drm_bridge_add/remove() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-1-bad7eba5d117@bootlin.com> References: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-0-bad7eba5d117@bootlin.com> In-Reply-To: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-0-bad7eba5d117@bootlin.com> To: Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: Dmitry Baryshkov , Anusha Srivatsa , Thomas Petazzoni , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Luca Ceresoli X-Mailer: b4 0.14.2 X-GND-State: clean X-GND-Score: -100 X-GND-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtddvgdektdehucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuifetpfffkfdpucggtfgfnhhsuhgsshgtrhhisggvnecuuegrihhlohhuthemuceftddunecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpefhfffugggtgffkfhgjvfevofesthejredtredtjeenucfhrhhomhepnfhutggrucevvghrvghsohhlihcuoehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmqeenucggtffrrghtthgvrhhnpeeiieeuvdfftefgueduleehueetgffgjeeitedtteetkeeuueeuueekveevvdeuveenucfkphepvdgrtddvmeeijedtmedvtddvtdemvggrtddumegsvgegudemleehvgejmeefgeefmeeludefvgenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepihhnvghtpedvrgdtvdemieejtdemvddtvddtmegvrgdtudemsggvgedumeelhegvjeemfeegfeemledufegvpdhhvghloheplgduledvrdduieekrddujeekrdejhegnpdhmrghilhhfrhhomheplhhutggrrdgtvghrvghsohhlihessghoohhtlhhinhdrtghomhdpnhgspghrtghpthhtohepudejpdhrtghpthhtoheprghirhhlihgvugesghhmrghilhdrtghomhdprhgtphhtthhopehrfhhoshhssehkvghrnhgvlhdrohhrghdprhgtphhtthhopehthhhomhgrshdrphgvthgriiiiohhnihessghoohhtlhhinhdrtghomhdprhgtphhtthhopehmrggrr hhtvghnrdhlrghnkhhhohhrshhtsehlihhnuhigrdhinhhtvghlrdgtohhmpdhrtghpthhtoheplhhinhhugidqkhgvrhhnvghlsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtohepmhhrihhprghrugeskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepshhimhhonhgrsehffhiflhhlrdgthhdprhgtphhtthhopegrshhrihhvrghtshesrhgvughhrghtrdgtohhm X-GND-Sasl: luca.ceresoli@bootlin.com drm_bridge_add() adds the bridge to the global bridge_list, so take a reference for that. Vice versa in drm_bridge_remove(). Reviewed-by: Maxime Ripard Signed-off-by: Luca Ceresoli --- Changes in v8: none Changes in v7: - in v6 this was part of "drm/bridge: add support for refcounted DRM bridges", now split to a separate patch --- drivers/gpu/drm/drm_bridge.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index d6ce7b4c019f415400bab8aa3d032638cba6cdc5..fa2b2457b16e145e3ace70c5398= 4937096d310d0 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -295,6 +295,8 @@ EXPORT_SYMBOL(__devm_drm_bridge_alloc); */ void drm_bridge_add(struct drm_bridge *bridge) { + drm_bridge_get(bridge); + mutex_init(&bridge->hpd_mutex); =20 if (bridge->ops & DRM_BRIDGE_OP_HDMI) @@ -342,6 +344,8 @@ void drm_bridge_remove(struct drm_bridge *bridge) mutex_unlock(&bridge_lock); =20 mutex_destroy(&bridge->hpd_mutex); + + drm_bridge_put(bridge); } EXPORT_SYMBOL(drm_bridge_remove); =20 --=20 2.49.0 From nobody Thu Oct 9 04:18:58 2025 Received: from relay5-d.mail.gandi.net (relay5-d.mail.gandi.net [217.70.183.197]) (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 EBF36284B3B for ; 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charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-2-bad7eba5d117@bootlin.com> References: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-0-bad7eba5d117@bootlin.com> In-Reply-To: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-0-bad7eba5d117@bootlin.com> To: Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: Dmitry Baryshkov , Anusha Srivatsa , Thomas Petazzoni , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Luca Ceresoli X-Mailer: b4 0.14.2 X-GND-State: clean X-GND-Score: -100 X-GND-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtddvgdektdehucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuifetpfffkfdpucggtfgfnhhsuhgsshgtrhhisggvnecuuegrihhlohhuthemuceftddunecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpefhfffugggtgffkfhgjvfevofesthejredtredtjeenucfhrhhomhepnfhutggrucevvghrvghsohhlihcuoehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmqeenucggtffrrghtthgvrhhnpeeiieeuvdfftefgueduleehueetgffgjeeitedtteetkeeuueeuueekveevvdeuveenucfkphepvdgrtddvmeeijedtmedvtddvtdemvggrtddumegsvgegudemleehvgejmeefgeefmeeludefvgenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepihhnvghtpedvrgdtvdemieejtdemvddtvddtmegvrgdtudemsggvgedumeelhegvjeemfeegfeemledufegvpdhhvghloheplgduledvrdduieekrddujeekrdejhegnpdhmrghilhhfrhhomheplhhutggrrdgtvghrvghsohhlihessghoohhtlhhinhdrtghomhdpnhgspghrtghpthhtohepudejpdhrtghpthhtoheprghirhhlihgvugesghhmrghilhdrtghomhdprhgtphhtthhopehrfhhoshhssehkvghrnhgvlhdrohhrghdprhgtphhtthhopehthhhomhgrshdrphgvthgriiiiohhnihessghoohhtlhhinhdrtghomhdprhgtphhtthhopehmrggrr hhtvghnrdhlrghnkhhhohhrshhtsehlihhnuhigrdhinhhtvghlrdgtohhmpdhrtghpthhtoheplhhinhhugidqkhgvrhhnvghlsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtohepmhhrihhprghrugeskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepshhimhhonhgrsehffhiflhhlrdgthhdprhgtphhtthhopegrshhrihhvrghtshesrhgvughhrghtrdgtohhm X-GND-Sasl: luca.ceresoli@bootlin.com drm_bridge_attach() adds the bridge to the encoder chain, so take a reference for that. Vice versa in drm_bridge_detach(). Reviewed-by: Maxime Ripard Signed-off-by: Luca Ceresoli --- Changes in v8: none Changes in v7: - in v6 this was part of "drm/bridge: add support for refcounted DRM bridges", now split to a separate patch --- drivers/gpu/drm/drm_bridge.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index fa2b2457b16e145e3ace70c53984937096d310d0..f001bbe95559aabf0aac9f25f89= 250ad4e1ad9c8 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -411,11 +411,17 @@ int drm_bridge_attach(struct drm_encoder *encoder, st= ruct drm_bridge *bridge, if (!encoder || !bridge) return -EINVAL; =20 - if (previous && (!previous->dev || previous->encoder !=3D encoder)) - return -EINVAL; + drm_bridge_get(bridge); =20 - if (bridge->dev) - return -EBUSY; + if (previous && (!previous->dev || previous->encoder !=3D encoder)) { + ret =3D -EINVAL; + goto err_put_bridge; + } + + if (bridge->dev) { + ret =3D -EBUSY; + goto err_put_bridge; + } =20 bridge->dev =3D encoder->dev; bridge->encoder =3D encoder; @@ -464,6 +470,8 @@ int drm_bridge_attach(struct drm_encoder *encoder, stru= ct drm_bridge *bridge, "failed to attach bridge %pOF to encoder %s\n", bridge->of_node, encoder->name); =20 +err_put_bridge: + drm_bridge_put(bridge); return ret; } EXPORT_SYMBOL(drm_bridge_attach); @@ -484,6 +492,7 @@ void drm_bridge_detach(struct drm_bridge *bridge) =20 list_del(&bridge->chain_node); bridge->dev =3D NULL; + drm_bridge_put(bridge); } =20 /** --=20 2.49.0 From nobody Thu Oct 9 04:18:58 2025 Received: from relay5-d.mail.gandi.net (relay5-d.mail.gandi.net [217.70.183.197]) (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 B8BB12836B4 for ; Fri, 20 Jun 2025 09:32:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.183.197 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; 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spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="VcssiXm/" Received: by mail.gandi.net (Postfix) with ESMTPSA id 34CF8432D6; Fri, 20 Jun 2025 09:32:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1750411958; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=j5btolVDOHRmFzcmVnFsjVK9eR6OLhoqT6hli50wu5w=; b=VcssiXm/RVUj3k2m8k8OX9B3++mP5KPy4JxUqoBbjo+EbHXAc6bYGRW6pSWdxysspmLEdS 3/Ita34EnR9sUZVNQZMsWv2knkFAQnPh5Ri9KsYaOwSwXYvW0WRO9IX0ERH//7teAfSsiA M+4r+Yhal8UT1PIDb7s9Q58oup489sLaled+BFALcyHEIkFZGGhYZiE59Rughr7rqln+GY Cs0EAvS+kIaX7TOzbn7E/bSTbX8a62YlfC/Q4qBKjMzj1U6m6LSE30+Ia5WTkxtOV46fJ2 5/rhnwHbXvNKs5aa1icbVcjT0D4ynH/uRJy6Ta2aJw1+vQqRcw3LoJOfTyP4eg== From: Luca Ceresoli Date: Fri, 20 Jun 2025 11:32:08 +0200 Subject: [PATCH 3/3] drm/bridge: add warning for bridges not using devm_drm_bridge_alloc() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-3-bad7eba5d117@bootlin.com> References: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-0-bad7eba5d117@bootlin.com> In-Reply-To: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-0-bad7eba5d117@bootlin.com> To: Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: Dmitry Baryshkov , Anusha Srivatsa , Thomas Petazzoni , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Luca Ceresoli X-Mailer: b4 0.14.2 X-GND-State: clean X-GND-Score: -100 X-GND-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtddvgdektdehucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuifetpfffkfdpucggtfgfnhhsuhgsshgtrhhisggvnecuuegrihhlohhuthemuceftddunecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpefhfffugggtgffkfhgjvfevofesthejredtredtjeenucfhrhhomhepnfhutggrucevvghrvghsohhlihcuoehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmqeenucggtffrrghtthgvrhhnpeeiieeuvdfftefgueduleehueetgffgjeeitedtteetkeeuueeuueekveevvdeuveenucfkphepvdgrtddvmeeijedtmedvtddvtdemvggrtddumegsvgegudemleehvgejmeefgeefmeeludefvgenucevlhhushhtvghrufhiiigvpedvnecurfgrrhgrmhepihhnvghtpedvrgdtvdemieejtdemvddtvddtmegvrgdtudemsggvgedumeelhegvjeemfeegfeemledufegvpdhhvghloheplgduledvrdduieekrddujeekrdejhegnpdhmrghilhhfrhhomheplhhutggrrdgtvghrvghsohhlihessghoohhtlhhinhdrtghomhdpnhgspghrtghpthhtohepudejpdhrtghpthhtoheprghirhhlihgvugesghhmrghilhdrtghomhdprhgtphhtthhopehrfhhoshhssehkvghrnhgvlhdrohhrghdprhgtphhtthhopehthhhomhgrshdrphgvthgriiiiohhnihessghoohhtlhhinhdrtghomhdprhgtphhtthhopehmrggrr hhtvghnrdhlrghnkhhhohhrshhtsehlihhnuhigrdhinhhtvghlrdgtohhmpdhrtghpthhtoheplhhinhhugidqkhgvrhhnvghlsehvghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtohepmhhrihhprghrugeskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepshhimhhonhgrsehffhiflhhlrdgthhdprhgtphhtthhopegrshhrihhvrghtshesrhgvughhrghtrdgtohhm X-GND-Sasl: luca.ceresoli@bootlin.com To the best of my knowledge, all drivers in the mainline kernel adding a DRM bridge are now converted to using devm_drm_bridge_alloc() for allocation and initialization. Among others this ensures initialization of the bridge refcount, allowing dynamic allocation lifetime. devm_drm_bridge_alloc() is now mandatory for all new bridges. Code using the old pattern ([devm_]kzalloc + filling the struct fields + drm_bridge_add) is not allowed anymore. Any drivers that might have been missed during the conversion, patches in flight towards mainline and out-of-tre drivers still using the old pattern will already be caught by a warning looking like: ------------[ cut here ]------------ refcount_t: addition on 0; use-after-free. WARNING: CPU: 2 PID: 83 at lib/refcount.c:25 refcount_warn_saturate+0x120= /0x148 [...] Call trace: refcount_warn_saturate+0x120/0x148 (P) drm_bridge_get.part.0+0x70/0x98 [drm] drm_bridge_add+0x34/0x108 [drm] sn65dsi83_probe+0x200/0x480 [ti_sn65dsi83] [...] This warning comes from the refcount code and happens because drm_bridge_add() is increasing the refcount, which is uninitialized and thus initially zero. Having a warning and the corresponding stack trace is surely useful, but the warning text does not clarify the root problem nor how to fix it. Add a DRM_WARN() just before increasing the refcount, so the log will be much more readable: [drm] DRM bridge corrupted or not allocated by devm_drm_bridge_alloc() ------------[ cut here ]------------ refcount_t: addition on 0; use-after-free. [...etc...] A DRM_WARN is used because drm_warn and drm_WARN require a struct drm_device pointer which is not yet available when adding a bridge. Do not print the dev_name() in the warning because struct drm_bridge has no pointer to the struct device. The affected driver should be easy to catch based on the following stack trace however. Signed-off-by: Luca Ceresoli --- This patch was added in v8 --- drivers/gpu/drm/drm_bridge.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index f001bbe95559aabf0aac9f25f89250ad4e1ad9c8..7d511c28608f1d8ea8fbb81d00e= fa9e227b02a13 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -295,6 +295,9 @@ EXPORT_SYMBOL(__devm_drm_bridge_alloc); */ void drm_bridge_add(struct drm_bridge *bridge) { + if (kref_read(&bridge->refcount) =3D=3D 0) + DRM_WARN("DRM bridge corrupted or not allocated by devm_drm_bridge_alloc= ()\n"); + drm_bridge_get(bridge); =20 mutex_init(&bridge->hpd_mutex); --=20 2.49.0