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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT 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 618DDC04AAF for ; Tue, 21 May 2019 15:44:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4113A21743 for ; Tue, 21 May 2019 15:44:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728857AbfEUPoV (ORCPT ); Tue, 21 May 2019 11:44:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59284 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728323AbfEUPoV (ORCPT ); Tue, 21 May 2019 11:44:21 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 53D0AC05E760; Tue, 21 May 2019 15:44:15 +0000 (UTC) Received: from redhat.com (unknown [10.20.6.178]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3DA9D17F34; Tue, 21 May 2019 15:44:13 +0000 (UTC) Date: Tue, 21 May 2019 11:44:11 -0400 From: Jerome Glisse To: Daniel Vetter Cc: DRI Development , Intel Graphics Development , LKML , Linux MM , Andrew Morton , Michal Hocko , Christian =?iso-8859-1?Q?K=F6nig?= , David Rientjes , Paolo Bonzini , Daniel Vetter Subject: Re: [PATCH 1/4] mm: Check if mmu notifier callbacks are allowed to fail Message-ID: <20190521154411.GD3836@redhat.com> References: <20190520213945.17046-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190520213945.17046-1-daniel.vetter@ffwll.ch> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Tue, 21 May 2019 15:44:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 20, 2019 at 11:39:42PM +0200, Daniel Vetter wrote: > Just a bit of paranoia, since if we start pushing this deep into > callchains it's hard to spot all places where an mmu notifier > implementation might fail when it's not allowed to. > > Inspired by some confusion we had discussing i915 mmu notifiers and > whether we could use the newly-introduced return value to handle some > corner cases. Until we realized that these are only for when a task > has been killed by the oom reaper. > > An alternative approach would be to split the callback into two > versions, one with the int return value, and the other with void > return value like in older kernels. But that's a lot more churn for > fairly little gain I think. > > Summary from the m-l discussion on why we want something at warning > level: This allows automated tooling in CI to catch bugs without > humans having to look at everything. If we just upgrade the existing > pr_info to a pr_warn, then we'll have false positives. And as-is, no > one will ever spot the problem since it's lost in the massive amounts > of overall dmesg noise. > > v2: Drop the full WARN_ON backtrace in favour of just a pr_warn for > the problematic case (Michal Hocko). > > v3: Rebase on top of Glisse's arg rework. > > v4: More rebase on top of Glisse reworking everything. > > Cc: Andrew Morton > Cc: Michal Hocko > Cc: "Christian König" > Cc: David Rientjes > Cc: Daniel Vetter > Cc: "Jérôme Glisse" > Cc: linux-mm@kvack.org > Cc: Paolo Bonzini > Reviewed-by: Christian König > Signed-off-by: Daniel Vetter Reviewed-by: Jérôme Glisse > --- > mm/mmu_notifier.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c > index ee36068077b6..c05e406a7cd7 100644 > --- a/mm/mmu_notifier.c > +++ b/mm/mmu_notifier.c > @@ -181,6 +181,9 @@ int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range) > pr_info("%pS callback failed with %d in %sblockable context.\n", > mn->ops->invalidate_range_start, _ret, > !mmu_notifier_range_blockable(range) ? "non-" : ""); > + if (!mmu_notifier_range_blockable(range)) > + pr_warn("%pS callback failure not allowed\n", > + mn->ops->invalidate_range_start); > ret = _ret; > } > } > -- > 2.20.1 >