From mboxrd@z Thu Jan 1 00:00:00 1970 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 BCA3A3B637E for ; Thu, 9 Apr 2026 09:57:24 +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=1775728647; cv=none; b=Of8RkJ0QAnNNoMGtD3KP1Vg78q3+dILpie86YVcFqSVRvDZcsOldpK11yVN25P2YUnVK3Lvu7Dd4+X2JGiD6jg4meYPqB+Q31Plu6df+MRR5pJOXYOvKd8GQyb/4N9/htPuWEyEfqfdaKjA22mrjxNEHlVpQnmC2O+zJ9k0Lh24= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775728647; c=relaxed/simple; bh=foKzo5tgGMP7iT0vnZ29YhDQ893+304njSr8HPh6cdk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Sli7HBDP/UMq4W5+l/t4NPpMYgdVtzaWOJCXsvBIanrZeEecc5jxX0Fq6M4Trv+AOflXXNjY7E/bBLGnK3V3iFFEAgQvku44fIl2mt1ODEdyn6hMgIaUoIrPhXYRhNH85qmlSgxvYRMZt4bzn0O1vij/zjGVQ4BIHo4p82eWA1c= 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=H4rAFGB7; 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="H4rAFGB7" Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-04.galae.net (Postfix) with ESMTPS id 40787C5B1A0; Thu, 9 Apr 2026 09:57:57 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 9983B5FDEB; Thu, 9 Apr 2026 09:57:22 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 823C61045024B; Thu, 9 Apr 2026 11:57:18 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1775728641; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:content-language:in-reply-to:references; bh=H4Duh/8RS/OPo8SoITHDOLmCgFlW4owZSO6Ia9g4olk=; b=H4rAFGB7hI3Xu7gkabvq+HMyx3YP0XZYenDDnoUhQiHt3JUCzyU/qyvG0hpB0M2/SKrUYv pIV78kIXCco19Ua1TuNed6fxMKGH4Y0NQ+R076b/emN1aTIlBKgjdTTQ6wvr48g4u3F0Sz SL7du88TLqa/2joZEn7Dmya0H73pi7BNYDAslAf/b67WTwTcHUiWuMIxKc+0lqe25xkmjB SkSWmf2J4FpS/PZhx29xlPTQmtrDwcsj2wmIlnuJ8jCVH10qplOGziFV0w83fZ8+D7E6Ro jvnmBZfpczzB/Ziu2qaYuH+p0m/FAe7EhTvXiotPDt6p338ighXaK7suxxD81g== Message-ID: <4fdc66a6-9429-4c80-8014-a09c492d6cf2@bootlin.com> Date: Thu, 9 Apr 2026 11:57:18 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 7/7] drm/bridge: prevent encoder chain changes in pre_enable/post_disable To: Luca Ceresoli , 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, Ian Ray References: <20260324-drm-bridge-alloc-encoder-chain-mutex-v5-0-8bf786c5c7e6@bootlin.com> <20260324-drm-bridge-alloc-encoder-chain-mutex-v5-7-8bf786c5c7e6@bootlin.com> Content-Language: en-US From: Louis Chauvet In-Reply-To: <20260324-drm-bridge-alloc-encoder-chain-mutex-v5-7-8bf786c5c7e6@bootlin.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Last-TLS-Session-Version: TLSv1.3 On 3/24/26 9:58 AM, Luca Ceresoli wrote: > 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 Reviewed-by: Louis Chauvet > --- > > 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 c76f3451af39..29231730e1f8 100644 > --- a/drivers/gpu/drm/drm_bridge.c > +++ b/drivers/gpu/drm/drm_bridge.c > @@ -867,6 +867,7 @@ void drm_atomic_bridge_chain_post_disable(struct drm_bridge *bridge, > > encoder = bridge->encoder; > > + mutex_lock(&encoder->bridge_chain_mutex); > list_for_each_entry_from(bridge, &encoder->bridge_chain, chain_node) { > limit = NULL; > > @@ -915,6 +916,7 @@ void drm_atomic_bridge_chain_post_disable(struct drm_bridge *bridge, > /* Jump all bridges that we have already post_disabled */ > bridge = limit; > } > + mutex_unlock(&encoder->bridge_chain_mutex); > } > EXPORT_SYMBOL(drm_atomic_bridge_chain_post_disable); > > @@ -961,6 +963,7 @@ void drm_atomic_bridge_chain_pre_enable(struct drm_bridge *bridge, > > encoder = bridge->encoder; > > + mutex_lock(&encoder->bridge_chain_mutex); > list_for_each_entry_reverse(iter, &encoder->bridge_chain, chain_node) { > if (iter->pre_enable_prev_first) { > next = iter; > @@ -1003,6 +1006,7 @@ void drm_atomic_bridge_chain_pre_enable(struct drm_bridge *bridge, > if (iter == bridge) > break; > } > + mutex_unlock(&encoder->bridge_chain_mutex); > } > EXPORT_SYMBOL(drm_atomic_bridge_chain_pre_enable); > >