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Fri, 16 Mar 2018 22:36:25 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:19055 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751372AbeCQCgY (ORCPT ); Fri, 16 Mar 2018 22:36:24 -0400 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 16 Mar 2018 19:36:24 -0700 Subject: Re: [PATCH 03/14] mm/hmm: HMM should have a callback before MM is destroyed v2 To: , CC: Andrew Morton , , Ralph Campbell , , Evgeny Baskakov , Mark Hairgrove References: <20180316191414.3223-1-jglisse@redhat.com> <20180316191414.3223-4-jglisse@redhat.com> X-Nvconfidentiality: public From: John Hubbard Message-ID: <7e87c1f9-5c1a-84fd-1f7f-55ffaaed8a66@nvidia.com> Date: Fri, 16 Mar 2018 19:36:23 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180316191414.3223-4-jglisse@redhat.com> X-Originating-IP: [10.110.48.28] X-ClientProxiedBy: HQMAIL107.nvidia.com (172.20.187.13) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 03/16/2018 12:14 PM, jglisse@redhat.com wrote: > From: Ralph Campbell > > +static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm) > +{ > + struct hmm *hmm = mm->hmm; > + struct hmm_mirror *mirror; > + struct hmm_mirror *mirror_next; > + > + down_write(&hmm->mirrors_sem); > + list_for_each_entry_safe(mirror, mirror_next, &hmm->mirrors, list) { > + list_del_init(&mirror->list); > + if (mirror->ops->release) > + mirror->ops->release(mirror); > + } > + up_write(&hmm->mirrors_sem); > +} > + OK, as for actual code review: This part of the locking looks good. However, I think it can race against hmm_mirror_register(), because hmm_mirror_register() will just add a new mirror regardless. So: thread 1 thread 2 -------------- ----------------- hmm_release hmm_mirror_register down_write(&hmm->mirrors_sem); // deletes all list items up_write unblocked: adds new mirror ...so I think we need a way to back out of any pending hmm_mirror_register() calls, as part of the .release steps, right? It seems hard for the device driver, which could be inside of hmm_mirror_register(), to handle that. Especially considering that right now, hmm_mirror_register() will return success in this case--so there is no indication that anything is wrong. Maybe hmm_mirror_register() could return an error (and not add to the mirror list), in such a situation, how's that sound? thanks, -- John Hubbard NVIDIA