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 X-Spam-Level: X-Spam-Status: No, score=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 87CA3C4361B for ; Mon, 14 Dec 2020 16:43:50 +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 CF5B7224D1 for ; Mon, 14 Dec 2020 16:43:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CF5B7224D1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=chris-wilson.co.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 216FB89BE8; Mon, 14 Dec 2020 16:43:49 +0000 (UTC) Received: from fireflyinternet.com (unknown [77.68.26.236]) by gabe.freedesktop.org (Postfix) with ESMTPS id BE72D89BE8; Mon, 14 Dec 2020 16:43:46 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from localhost (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP (TLS) id 23322814-1500050 for multiple; Mon, 14 Dec 2020 16:43:41 +0000 MIME-Version: 1.0 In-Reply-To: <5f0cb1c5-f925-8928-c450-a19d1547af8d@intel.com> References: <20201208170205.2039137-1-chris@chris-wilson.co.uk> <5f0cb1c5-f925-8928-c450-a19d1547af8d@intel.com> From: Chris Wilson To: Matthew Auld , intel-gfx@lists.freedesktop.org Date: Mon, 14 Dec 2020 16:43:42 +0000 Message-ID: <160796422254.13039.11905877707215718456@build.alporthouse.com> User-Agent: alot/0.9 Subject: Re: [Intel-gfx] [PATCH i-g-t] i915/gem_vm_create: Race vm-destroy against object free 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: , Cc: igt-dev@lists.freedesktop.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Quoting Matthew Auld (2020-12-14 15:52:06) > On 08/12/2020 17:02, Chris Wilson wrote: > > Matthew postulated that we should be able to hit a race in > > __i915_vm_close() between the RCU object free and vma unbind viz > > > > GEM_BUG_ON(!list_empty(&vm->bound_list)); > > > > due to the effect of leaving the vma on the list if we are unable to > > obtain the kref to the object. Let's try and find that race. > > Hmm, what's the idea behind the bound_list stuff in __i915_vm_close(), > from the looks of it vm->open is always > 0 anyway for the lifetime of > the vm(?), so not sure if it's even possible to hit that path, at least > for direct userspace interactions. >From userspace, the intent was to track vm->open. i.e. we could not close the whole vm as it was being used by execbuf. With the individual vma holding a reference to the vm to prevent it being freed while still active on the GPU. > I guess I was half expecting the > vm_destroy ioctl or similar, to also call i915_vm_close() at some point, > to match vm_create, and not just drop the vm ref. Right, each user vm_id is only a reference to a vm, and the user may have multiple vm_id to the same vm. So there's an ambiguity that prevents us from immediately closing the vm on destroy, and so just manage references instead. > So looks like > __i915_vm_close() is only potentially interesting for kernel internal users? Hmm. There's a call to i915_vm_close from context_close (and on changing the context vm). And there definitely can be vma still bound at that point, and those vma still linked into the obj->vma_list. So I think the pruning is still relevant for GEM contexts. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx