From nobody Sun Feb 8 19:39:35 2026 Received: from smtpout-04.galae.net (smtpout-04.galae.net [185.171.202.116]) (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 11B35352C2D for ; Tue, 13 Jan 2026 18:47:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.171.202.116 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768330067; cv=none; b=WyMV1h/qqh8BB5FbwCrrF07Ubv2At18r6kkyI5wn8BLZPrrmTQKzpWnZ0DT0qc8A/FNd/HAbcgZZIh3VNgUKv69TpvlMWwSL4ka07poF5nK3IOkSF5cbhx6ZQHXdFV5+7vMCsjNtOq9v0L277aqwdobZRDCPW3r8EQKPCgueMWo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768330067; c=relaxed/simple; bh=wIyjkJuGuBNELHnuKB+mmE0kYmh9zRXfcaF4nIm1Gz4=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=Hqi/t8Egcy2WlLLdSt8lMH5khN4TAveUWrox0YZJdYG3pZKrBl+aKqrZkZ2kdQ17xiVi3iDqnj7AqW7mYjARZ0DWucAy3hvkfwrFPS8wJJHz/Rynr497BLgB4UgeaE3oApmc9CwCXH1zFeINlG39oZVq0SZLWZ/w54qlXtlOO4g= 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=uydhV+vM; arc=none smtp.client-ip=185.171.202.116 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="uydhV+vM" Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-04.galae.net (Postfix) with ESMTPS id F3781C1ECB8; Tue, 13 Jan 2026 18:47:12 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 87EFB60701; Tue, 13 Jan 2026 18:47:39 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 10FD9103C871F; Tue, 13 Jan 2026 19:47:36 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1768330058; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=dG/J7ABnbSTu61X3mrMuyDFuZTrdXx8E+cS1ACIsDWw=; b=uydhV+vM9q2P5fWZBH+W/KTjwFFJyvp8rsTykluvNinkGHFqdhQF8xsTpB9SqJWc8oPZAX jhZJgXgafJRYZ4D9EfFkDV+Onv9wd9DR8/NDyOAl25u7/CbHRMlKqR2nCYtkGvvySsio/5 scQ3K9bVFgXa7dvs3vecE84PNAKemjXw9J/7EXmOuJl28tOwYG/meSE8MNWOC+GszcHnma NrkACgNI3nxJ3Ld7fERqR4ROWtvlRFHJ72cxeK3TWSdPU9Y3wPXl+8Y3UXco0krtFhRMPY mLkSX7vBOLkwgFkNk+befeN+KBG2wkwrC3fpN38KJiZFtnM0W1SrEkeVEpENQA== From: Luca Ceresoli Date: Tue, 13 Jan 2026 19:47:18 +0100 Subject: [PATCH RESEND v4 7/7] drm/bridge: prevent encoder chain changes in pre_enable/post_disable 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: <20260113-drm-bridge-alloc-encoder-chain-mutex-v4-7-60f3135adc45@bootlin.com> References: <20260113-drm-bridge-alloc-encoder-chain-mutex-v4-0-60f3135adc45@bootlin.com> In-Reply-To: <20260113-drm-bridge-alloc-encoder-chain-mutex-v4-0-60f3135adc45@bootlin.com> To: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec Cc: Hui Pu , Thomas Petazzoni , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Luca Ceresoli , Ian Ray X-Mailer: b4 0.14.3 X-Last-TLS-Session-Version: TLSv1.3 Take the encoder chain mutex while iterating over the encoder chain in drm_atomic_bridge_chain_pre_enable() and drm_atomic_bridge_chain_post_disable() to ensure the lists won't change while being inspected. These functions have nested list_for_each_*() loops, which makes them complicated. list_for_each_entry_from() loops could be replaced by drm_for_each_bridge_in_chain_from(), but it would not work in a nested way in its current implementation. Besides, there is no "_reverse" variant of drm_for_each_bridge_in_chain_from(). Keep code simple and readable by explicitly locking around the outer loop. Thankfully there are no break or return points inside the loops, so the change is trivial and readable. Reviewed-by: Maxime Ripard Signed-off-by: Luca Ceresoli --- Changes in v3: - Lock encoder->bridge_chain_mutex directly, no wrappers - Improved commit message Changes in v2: - Improved commit message --- 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 eca138eadbc5..76895b0f84d3 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -769,6 +769,7 @@ void drm_atomic_bridge_chain_post_disable(struct drm_br= idge *bridge, =20 encoder =3D bridge->encoder; =20 + mutex_lock(&encoder->bridge_chain_mutex); list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) { limit =3D NULL; =20 @@ -817,6 +818,7 @@ void drm_atomic_bridge_chain_post_disable(struct drm_br= idge *bridge, /* Jump all bridges that we have already post_disabled */ bridge =3D limit; } + mutex_unlock(&encoder->bridge_chain_mutex); } EXPORT_SYMBOL(drm_atomic_bridge_chain_post_disable); =20 @@ -863,6 +865,7 @@ void drm_atomic_bridge_chain_pre_enable(struct drm_brid= ge *bridge, =20 encoder =3D bridge->encoder; =20 + mutex_lock(&encoder->bridge_chain_mutex); list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) { if (iter->pre_enable_prev_first) { next =3D iter; @@ -905,6 +908,7 @@ void drm_atomic_bridge_chain_pre_enable(struct drm_brid= ge *bridge, if (iter =3D=3D bridge) break; } + mutex_unlock(&encoder->bridge_chain_mutex); } EXPORT_SYMBOL(drm_atomic_bridge_chain_pre_enable); =20 --=20 2.52.0