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 66533C44512 for ; Thu, 16 Jul 2026 20:31:14 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id ACF7210E3E5; Thu, 16 Jul 2026 20:31:13 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="HwYrdElh"; dkim-atps=neutral Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by gabe.freedesktop.org (Postfix) with ESMTPS id 56DC910E3E5 for ; Thu, 16 Jul 2026 20:31:12 +0000 (UTC) Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 663DF60A5E; Thu, 16 Jul 2026 20:31:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E559D1F000E9; Thu, 16 Jul 2026 20:31:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784233871; bh=v2MjMfPLTrFGg6XvjdkhMC0lptHmvwtkp+iQ3rXdUWY=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=HwYrdElh9oEnXBac/IMP8S+S/rE3HO2E9auluK4DnQB3OCWBoKd+OKTo5Ir7CNu8u v5mn8QwNNWnCqHCQ3Kkqio9SgFlI330XkrCY5m+w7xTwxcpJbnR0fErXGhQVd5DsNB b7ays5/MWQ3HeLPKNMk6dlfz2jYijOn7GkHSQBmgvnWaOwLSuhwWTUUisYHqGRJEtR dJ+hCx7hY+kyw0u3x5dz97HhlUwU1XCFO5fYfJtzYKz09OEbSwhMfl/IO6yHQzPacK FEFJY0ev0YS+xT0yljD2Cz5B3Cervl5fn90cEs0eYM9deG8ktpNyd97X/7l8fVpgag Cw55i3pWTNKVA== From: sashiko-bot@kernel.org Subject: Re: [PATCH v5 01/10] drm/msm: Fix barriers accessing ctx vm To: "Rob Clark" Cc: dri-devel@lists.freedesktop.org In-Reply-To: <20260716201538.365824-2-robin.clark@oss.qualcomm.com> References: <20260716201538.365824-1-robin.clark@oss.qualcomm.com> <20260716201538.365824-2-robin.clark@oss.qualcomm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 16 Jul 2026 20:31:10 +0000 Message-Id: <20260716203110.E559D1F000E9@smtp.kernel.org> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Thank you for your contribution! Sashiko AI review found 2 potential issue(= s) to consider: Pre-existing issues: - [High] MSM VM Lazy Initialization Violation / NULL Pointer Dereference in= `msm_ioctl_gem_submit` and `msm_gem_new_handle` - [High] Incomplete barrier fix: `msm_gem_close()` performs a lockless plai= n read of `ctx->vm` leading to a data race -- --- Patch [1]: [PATCH v5 01/10] drm/msm: Fix barriers accessing ctx vm --- commit fdc4f5db0f02ec8c94395cb949b516d777a3923b Author: Rob Clark drm/msm: Fix barriers accessing ctx vm This patch fixes a race condition by using smp_load_acquire and smp_store_release when accessing ctx->vm. This prevents callers from seeing a partially initialized vm. > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c > index 79f78e7e16e9d..3c8b5083a1fbe 100644 > --- a/drivers/gpu/drm/msm/msm_drv.c > +++ b/drivers/gpu/drm/msm/msm_drv.c > @@ -225,18 +225,19 @@ struct drm_gpuvm *msm_context_vm(struct drm_device = *dev, struct msm_context *ctx > { > static DEFINE_MUTEX(init_lock); > struct msm_drm_private *priv =3D dev->dev_private; > + struct drm_gpuvm *vm =3D smp_load_acquire(&ctx->vm); [Severity: High] This isn't a bug introduced by this patch, but since we are fixing the barriers for ctx->vm here, do we also need to update msm_gem_close()? It appears to perform a lockless plain read of ctx->vm: drivers/gpu/drm/msm/msm_gem.c:msm_gem_close() { ... if (!ctx->vm) return; /* ... */ msm_gem_lock_vm_and_obj(&exec, obj, ctx->vm); ... } Could this race with the smp_store_release() during VM creation and observe a partially initialized VM object? [Severity: High] This is a pre-existing issue, but I noticed there are still direct accesses to ctx->vm instead of using msm_context_vm() for lazy initialization. For example, in msm_ioctl_gem_submit(): drivers/gpu/drm/msm/msm_gem_submit.c:msm_ioctl_gem_submit() { ... if (to_msm_vm(ctx->vm)->unusable) ... } And also in msm_gem_new_handle(): drivers/gpu/drm/msm/msm_gem.c:msm_gem_new_handle() { ... struct drm_gem_object *r_obj =3D drm_gpuvm_resv_obj(ctx->vm); ... } If ctx->vm is NULL before initialization, could these direct accesses result in a NULL pointer dereference? > =20 > /* Once ctx->vm is created it is valid for the lifetime of the context:= */ > - if (ctx->vm) > - return ctx->vm; > + if (vm) > + return vm; > + > + guard(mutex)(&init_lock); > =20 > - mutex_lock(&init_lock); > if (!ctx->vm) { > - ctx->vm =3D msm_gpu_create_private_vm( > + vm =3D msm_gpu_create_private_vm( > priv->gpu, current, !ctx->userspace_managed_vm); > - > + smp_store_release(&ctx->vm, vm); > } > - mutex_unlock(&init_lock); > =20 > return ctx->vm; > } --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260716201538.3658= 24-1-robin.clark@oss.qualcomm.com?part=3D1