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In this context it means we >> are dereferencing a __rcu tagged pointer directly. > > Better use imperative here, e.g. "Fix a sparse warning ...". > > Wouldn't ask you to send a v3 for that alone... > >> >> We should not be directly dereferencing a rcu pointer, rather we should >> be using rcu helper function rcu_dereferece() inside rcu read critical >> section to get a normal pointer which can be dereferenced. > > ...but this doesn't seem accurate anymore as well. > > - Danilo > >> >> I tested with qemu with this command >> qemu-system-x86_64 \ >>     -m 2G \ >>     -smp 2 \ >>     -kernel bzImage \ >>     -append "console=ttyS0 root=/dev/sda earlyprintk=serial >> net.ifnames=0" \ >>     -drive file=bullseye.img,format=raw \ >>     -net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \ >>     -net nic,model=e1000 \ >>     -enable-kvm \ >>     -nographic \ >>     -pidfile vm.pid \ >>     2>&1 | tee vm.log >> with lockdep enabled. >> >> Signed-off-by: Abhinav Singh >> --- >> v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and >> also removed the rcu locking and unlocking function call. >> >>   drivers/gpu/drm/nouveau/nv04_fence.c | 2 +- >>   1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/nouveau/nv04_fence.c >> b/drivers/gpu/drm/nouveau/nv04_fence.c >> index 5b71a5a5cd85..cdbc75e3d1f6 100644 >> --- a/drivers/gpu/drm/nouveau/nv04_fence.c >> +++ b/drivers/gpu/drm/nouveau/nv04_fence.c >> @@ -39,7 +39,7 @@ struct nv04_fence_priv { >>   static int >>   nv04_fence_emit(struct nouveau_fence *fence) >>   { >> -    struct nvif_push *push = fence->channel->chan.push; >> +    struct nvif_push *push = unrcu_pointer(fence->channel)->chan.push; >>       int ret = PUSH_WAIT(push, 2); >>       if (ret == 0) { >>           PUSH_NVSQ(push, NV_SW, 0x0150, fence->base.seqno); > Hi maintainers thanks a lot for reviewing this patch. I think I should fix my mistake by sending in another patch so that the code changes and description matches. So should I send another patch ? Thank You, Abhinav Singh From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 572ACC4706C for ; Tue, 16 Jan 2024 11:48:04 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 100E710E4D8; Tue, 16 Jan 2024 11:47:37 +0000 (UTC) Received: from mail-pg1-x52a.google.com (mail-pg1-x52a.google.com [IPv6:2607:f8b0:4864:20::52a]) by gabe.freedesktop.org (Postfix) with ESMTPS id A201710E093; Mon, 13 Nov 2023 18:55:30 +0000 (UTC) Received: by mail-pg1-x52a.google.com with SMTP id 41be03b00d2f7-58962bf3f89so320395a12.0; Mon, 13 Nov 2023 10:55:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1699901730; x=1700506530; darn=lists.freedesktop.org; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=G+f4rJoyzPIE0y6h0wORDQt+kRBF7nK+PXXMCBjyvGI=; b=MZtATveJ/end93gWzTAs4XgVkY4Co/if2JQRZLQFt4xkSbimbiYHCEqcT8zU9LFBay trPaU81pyJMYoxZp8BtzHUTdMfa9fQPlvAoGE/7iZ83D3E51GEn4gFJ4JktmCZcAJnJE ojvBLlxZ0OD7Urr/7+k9eSzp0a16uv0To9hKliR/uua3DAZSgu+C2MquqeykHm6/UE0m UaDlv6rnviG2UWw4aPeIWV1W3de5DhYGib/vHwDZymDEnnG6TPhGoYiIg9cYEeIM4RMd f7VCnqhh5NNA8X103BNZqRdRko6xv/8Ki39pxopB3+0o2/LTLUktVzYxRz3DRBy/1zRY JX/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699901730; x=1700506530; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=G+f4rJoyzPIE0y6h0wORDQt+kRBF7nK+PXXMCBjyvGI=; b=H+oC9D4/2cr9OaFshKhxo84V2tzWZ54G1wuHHDO0GFkU3z99Fn2UJiBwf048Cm0ZM3 dmnYVvHfA4U2LWh7a+/wIYqjMwXs5C7ZHeKsS35szRpJKE1g4m2qQ0CmIdIZpvFE1yGQ i0hAlZVNKVSZmsoyACU3yNHNeBVydwMoQVZeI5PgGNAVJmMI4wP+jdfrYMKjbaSfnkPK nkusbS2qGOz/bRYysci8LnjQT5ZpJmZ5rwLpXWljeEqOCnXVoCj31tHyWSLMXCl7xHsf 3S+c3r61T5aWEx2oLahfc3qq1ASag3lhUnBXVfu9SrRD0Lu8x4GIhDAqf2VhWPWG3qYf naqg== X-Gm-Message-State: AOJu0YxNosQlspZlMXWqLazheOguLT6wfaWrxsRz3+qH49EXfWRG1b4e 6armH2zj8PRRXR8PpJVyEb8= X-Google-Smtp-Source: AGHT+IE5duZlYWLgqLzfa5RiDEmFjpMM0G68cLOdfphgOn3YyS8OIU25TqGIK0nk9u3XKZly5FW4rQ== X-Received: by 2002:a05:6a20:9381:b0:163:d382:ba84 with SMTP id x1-20020a056a20938100b00163d382ba84mr130227pzh.5.1699901730166; Mon, 13 Nov 2023 10:55:30 -0800 (PST) Received: from [192.168.0.152] ([103.75.161.210]) by smtp.gmail.com with ESMTPSA id ka27-20020a056a00939b00b0069102aa1918sm4091818pfb.48.2023.11.13.10.55.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Nov 2023 10:55:29 -0800 (PST) Message-ID: Date: Tue, 14 Nov 2023 00:25:24 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer Content-Language: en-US To: Danilo Krummrich , kherbst@redhat.com, lyude@redhat.com, airlied@gmail.com, daniel@ffwll.ch References: <20231113184238.3276835-1-singhabhinav9051571833@gmail.com> <373d97fc-0612-40da-ae9d-6702aa4483ba@redhat.com> From: Abhinav Singh In-Reply-To: <373d97fc-0612-40da-ae9d-6702aa4483ba@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Tue, 16 Jan 2024 11:47:29 +0000 X-BeenThere: nouveau@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Nouveau development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: nouveau@lists.freedesktop.org, linux-kernel-mentees@lists.linuxfoundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Errors-To: nouveau-bounces@lists.freedesktop.org Sender: "Nouveau" On 11/14/23 00:19, Danilo Krummrich wrote: > Hi, > > thanks for sending a v2. > > On 11/13/23 19:42, Abhinav Singh wrote: >> This patch fixes a sparse warning with this message >> "warning:dereference of noderef expression". In this context it means we >> are dereferencing a __rcu tagged pointer directly. > > Better use imperative here, e.g. "Fix a sparse warning ...". > > Wouldn't ask you to send a v3 for that alone... > >> >> We should not be directly dereferencing a rcu pointer, rather we should >> be using rcu helper function rcu_dereferece() inside rcu read critical >> section to get a normal pointer which can be dereferenced. > > ...but this doesn't seem accurate anymore as well. > > - Danilo > >> >> I tested with qemu with this command >> qemu-system-x86_64 \ >>     -m 2G \ >>     -smp 2 \ >>     -kernel bzImage \ >>     -append "console=ttyS0 root=/dev/sda earlyprintk=serial >> net.ifnames=0" \ >>     -drive file=bullseye.img,format=raw \ >>     -net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \ >>     -net nic,model=e1000 \ >>     -enable-kvm \ >>     -nographic \ >>     -pidfile vm.pid \ >>     2>&1 | tee vm.log >> with lockdep enabled. >> >> Signed-off-by: Abhinav Singh >> --- >> v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and >> also removed the rcu locking and unlocking function call. >> >>   drivers/gpu/drm/nouveau/nv04_fence.c | 2 +- >>   1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/nouveau/nv04_fence.c >> b/drivers/gpu/drm/nouveau/nv04_fence.c >> index 5b71a5a5cd85..cdbc75e3d1f6 100644 >> --- a/drivers/gpu/drm/nouveau/nv04_fence.c >> +++ b/drivers/gpu/drm/nouveau/nv04_fence.c >> @@ -39,7 +39,7 @@ struct nv04_fence_priv { >>   static int >>   nv04_fence_emit(struct nouveau_fence *fence) >>   { >> -    struct nvif_push *push = fence->channel->chan.push; >> +    struct nvif_push *push = unrcu_pointer(fence->channel)->chan.push; >>       int ret = PUSH_WAIT(push, 2); >>       if (ret == 0) { >>           PUSH_NVSQ(push, NV_SW, 0x0150, fence->base.seqno); > Hi maintainers thanks a lot for reviewing this patch. I think I should fix my mistake by sending in another patch so that the code changes and description matches. So should I send another patch ? Thank You, Abhinav Singh