From patchwork Thu Sep 2 14:20:49 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Daniel Vetter X-Patchwork-Id: 12471801 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7630C432BE for ; Thu, 2 Sep 2021 14:21:21 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id B2B3661053 for ; Thu, 2 Sep 2021 14:21:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org B2B3661053 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 775AD6E56A; Thu, 2 Sep 2021 14:21:12 +0000 (UTC) Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) by gabe.freedesktop.org (Postfix) with ESMTPS id 737226E566 for ; Thu, 2 Sep 2021 14:21:11 +0000 (UTC) Received: by mail-wm1-x32d.google.com with SMTP id i3so1401066wmq.3 for ; Thu, 02 Sep 2021 07:21:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=oRVf9sbWz+z/GcsknHSTFYjsqPuEDYgjvOz54sSSPjg=; b=JwD5QvsT8ZjD3I6QXYH2bB9jVdSgPdiDXtezHCI74BIfVKSFiZYFbDV5MzC6cVcEcL kZCsrccx8dKAx9vwVpM5zGNMDMri86vUToJ9KCZRfyJszTjYFLVA6i1woZ0vnL6EeUbf hxc60KRFvzd4V5wB9KJda/bajbw+qQOgn7+vM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=oRVf9sbWz+z/GcsknHSTFYjsqPuEDYgjvOz54sSSPjg=; b=gh9kbzbiV+PrQPn2B/WuSJYhCUMKU7TPC3d6Q679d5UKEVysQbiRlatyQF3rE17TVL b6Ccm7nOZXTIOwXpT9oNwl2YiLCGTpPwW26HYxdkAIya476AMxxIrBkKscR7qglMxUxm /jGMEK5VwbVQsOKOZnmH6rnTDjdbp7VpoVdDjma+trx4lGsB47JYx1Ugv7A+9tjC5VIQ W+liSScIXew3Bfh/H4imqFtWCFqj1O27ksYD026ztxnxcFIohZWhi638J1jC3pmC3zgI vkCjwNzqi5zdF5YlaUR0Jcc1harqeddaaK2Jvl8EuSbHr3E2NXvWZI3oiVRhRzW2yd6C aiMA== X-Gm-Message-State: AOAM530sDc/5lPYf8DXXnX9XE2V34F0SjNGXsSnSeQxylgFZBi4KD5uW vYyIigs0rm7DtPHIRPmt3ZtU9w== X-Google-Smtp-Source: ABdhPJxL0hZrc6Rly1WFLMVZBfxn3WkJWmR+yGRlhJMIuIyJRX+wOXB4BaYLkNyB+U0BHroOitECMw== X-Received: by 2002:a05:600c:4b88:: with SMTP id e8mr3444010wmp.164.1630592470077; Thu, 02 Sep 2021 07:21:10 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id l2sm1841811wmi.1.2021.09.02.07.21.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Sep 2021 07:21:09 -0700 (PDT) From: Daniel Vetter To: DRI Development Cc: Intel Graphics Development , Daniel Vetter , Maarten Lankhorst , Jason Ekstrand , Chris Wilson , Tvrtko Ursulin , Joonas Lahtinen , Matthew Brost , Matthew Auld , =?utf-8?q?Thomas_Hellstr=C3=B6m?= , Lionel Landwerlin , Dave Airlie , Daniel Vetter Date: Thu, 2 Sep 2021 16:20:49 +0200 Message-Id: <20210902142057.929669-3-daniel.vetter@ffwll.ch> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210902142057.929669-1-daniel.vetter@ffwll.ch> References: <20210902142057.929669-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Subject: [Intel-gfx] [PATCH 03/11] drm/i915: Keep gem ctx->vm alive until the final put X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" The comment added in commit b81dde719439c8f09bb61e742ed95bfc4b33946b Author: Chris Wilson Date: Tue May 21 22:11:29 2019 +0100 drm/i915: Allow userspace to clone contexts on creation and moved in commit 27dbae8f36c1c25008b7885fc07c57054b7dfba3 Author: Chris Wilson Date: Wed Nov 6 09:13:12 2019 +0000 drm/i915/gem: Safely acquire the ctx->vm when copying suggested that i915_address_space were at least intended to be managed through SLAB_TYPESAFE_BY_RCU: * This ppgtt may have be reallocated between * the read and the kref, and reassigned to a third * context. In order to avoid inadvertent sharing * of this ppgtt with that third context (and not * src), we have to confirm that we have the same * ppgtt after passing through the strong memory * barrier implied by a successful * kref_get_unless_zero(). But extensive git history search has not brough any such reuse to light. What has come to light though is that ever since commit 2850748ef8763ab46958e43a4d1c445f29eeb37d Author: Chris Wilson Date: Fri Oct 4 14:39:58 2019 +0100 drm/i915: Pull i915_vma_pin under the vm->mutex (yes this commit is earlier) the final i915_vma_put call has been moved from i915_gem_context_free (now called _release) to context_close, which means it's not actually safe anymore to access the ctx->vm pointer without lock helds, because it might disappear at any moment. Note that superficially things all still work, because the i915_address_space is RCU protected since commit b32fa811156328aea5a3c2ff05cc096490382456 Author: Chris Wilson Date: Thu Jun 20 19:37:05 2019 +0100 drm/i915/gtt: Defer address space cleanup to an RCU worker except the very clever macro above (which is designed to protected against object reuse due to SLAB_TYPESAFE_BY_RCU or similar tricks) results in an endless loop if the refcount of the ctx->vm ever permanently drops to 0. Which it totally now can. Fix that by moving the final i915_vm_put to where it should be. Note that i915_gem_context is rcu protected, but _only_ the final kfree. This means anyone who chases a pointer to a gem ctx solely under the protection can pretty only call kref_get_unless_zero(). This seems to be pretty much the case, aside from a bunch of cases that consult the scheduling information without any further protection. Reviewed-by: Maarten Lankhorst Cc: Jason Ekstrand Cc: Chris Wilson Cc: Tvrtko Ursulin Cc: Joonas Lahtinen Cc: Matthew Brost Cc: Matthew Auld Cc: Maarten Lankhorst Cc: "Thomas Hellström" Cc: Lionel Landwerlin Cc: Dave Airlie Fixes: 2850748ef876 ("drm/i915: Pull i915_vma_pin under the vm->mutex") Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/gem/i915_gem_context.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index 5a053cf14948..12e2de1db1a2 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -990,6 +990,7 @@ static void i915_gem_context_release_work(struct work_struct *work) { struct i915_gem_context *ctx = container_of(work, typeof(*ctx), release_work); + struct i915_address_space *vm; trace_i915_context_free(ctx); GEM_BUG_ON(!i915_gem_context_is_closed(ctx)); @@ -997,6 +998,10 @@ static void i915_gem_context_release_work(struct work_struct *work) if (ctx->syncobj) drm_syncobj_put(ctx->syncobj); + vm = i915_gem_context_vm(ctx); + if (vm) + i915_vm_put(vm); + mutex_destroy(&ctx->engines_mutex); mutex_destroy(&ctx->lut_mutex); @@ -1220,8 +1225,15 @@ static void context_close(struct i915_gem_context *ctx) set_closed_name(ctx); vm = i915_gem_context_vm(ctx); - if (vm) + if (vm) { + /* i915_vm_close drops the final reference, which is a bit too + * early and could result in surprises with concurrent + * operations racing with thist ctx close. Keep a full reference + * until the end. + */ + i915_vm_get(vm); i915_vm_close(vm); + } ctx->file_priv = ERR_PTR(-EBADF);