Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752500AbdLMK0o (ORCPT ); Wed, 13 Dec 2017 05:26:44 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:36165 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751508AbdLMK0j (ORCPT ); Wed, 13 Dec 2017 05:26:39 -0500 Subject: Re: [patch 1/2] mm, mmu_notifier: annotate mmu notifiers with blockable invalidate callbacks To: =?UTF-8?Q?Christian_K=c3=b6nig?= , David Rientjes , Dimitri Sivanich Cc: Andrew Morton , Michal Hocko , Andrea Arcangeli , Benjamin Herrenschmidt , Paul Mackerras , Oded Gabbay , Alex Deucher , David Airlie , Joerg Roedel , Doug Ledford , Jani Nikula , Mike Marciniszyn , Sean Hefty , Dimitri Sivanich , Boris Ostrovsky , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , LKML , linux-mm References: <20171212200542.GJ5848@hpe.com> From: Tetsuo Handa Message-ID: Date: Wed, 13 Dec 2017 19:26:31 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1834 Lines: 38 On 2017/12/13 18:34, Christian König wrote: > Am 12.12.2017 um 22:28 schrieb David Rientjes: >> On Tue, 12 Dec 2017, Dimitri Sivanich wrote: >> >>>> --- a/drivers/misc/sgi-gru/grutlbpurge.c >>>> +++ b/drivers/misc/sgi-gru/grutlbpurge.c >>>> @@ -298,6 +298,7 @@ struct gru_mm_struct *gru_register_mmu_notifier(void) >>>> return ERR_PTR(-ENOMEM); >>>> STAT(gms_alloc); >>>> spin_lock_init(&gms->ms_asid_lock); >>>> + gms->ms_notifier.flags = 0; >>>> gms->ms_notifier.ops = &gru_mmuops; >>>> atomic_set(&gms->ms_refcnt, 1); >>>> init_waitqueue_head(&gms->ms_wait_queue); >>>> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c >>> There is a kzalloc() just above this: >>> gms = kzalloc(sizeof(*gms), GFP_KERNEL); >>> >>> Is that not sufficient to clear the 'flags' field? >>> >> Absolutely, but whether it is better to explicitly document that the mmu >> notifier has cleared flags, i.e. there are no blockable callbacks, is >> another story. I can change it if preferred. > > Actually I would invert the new flag, in other words specify that an MMU notifier will never sleep. > > The first reason is that we have 8 blocking notifiers and 5 not blocking if I counted right. So it is actually more common to sleep than not to. > > The second reason is to be conservative and assume the worst, e.g. that the flag is forgotten when a new notifier is added. I agree. Some out of tree module might forget to set the flags. Although you don't need to fix out of tree modules, as a troubleshooting staff at a support center, I want to be able to identify the careless module. I guess specifying the flags at register function would be the best, for an attempt to call register function without knowing this change will simply results in a build failure.