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=-8.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,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 1B43EC04EB8 for ; Mon, 10 Dec 2018 13:28:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CD11720870 for ; Mon, 10 Dec 2018 13:28:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544448483; bh=8y/wS72TrQnG6ceV2uN0AYUwEqq0tkxIHOzdds83f4g=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=tEdSvFxCs1xM2EMLlMPN91SIAtMpuwpmXyldncKJIwlapC9UXSoJVypimFsdxZNNd sFlq2UXNRWemrqWPkewpybF9QwnFftXVpTQ/hgUzt85KoMZLNryHnk8FZu8neeBZdN DS10l+vXvhtqx4Gcd7BbEb1VOrXG3IqOjE5LEGMg= DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CD11720870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727437AbeLJN2C (ORCPT ); Mon, 10 Dec 2018 08:28:02 -0500 Received: from mx2.suse.de ([195.135.220.15]:57462 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726305AbeLJN2C (ORCPT ); Mon, 10 Dec 2018 08:28:02 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 65A55AE0B; Mon, 10 Dec 2018 13:28:00 +0000 (UTC) Date: Mon, 10 Dec 2018 14:27:59 +0100 From: Michal Hocko To: Daniel Vetter Cc: Intel Graphics Development , DRI Development , LKML , linux-mm@kvack.org, Andrew Morton , Christian =?iso-8859-1?Q?K=F6nig?= , David Rientjes , =?iso-8859-1?B?Suly9G1l?= Glisse , Paolo Bonzini , Daniel Vetter Subject: Re: [PATCH 1/4] mm: Check if mmu notifier callbacks are allowed to fail Message-ID: <20181210132759.GP1286@dhcp22.suse.cz> References: <20181210103641.31259-1-daniel.vetter@ffwll.ch> <20181210103641.31259-2-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: <20181210103641.31259-2-daniel.vetter@ffwll.ch> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 10-12-18 11:36:38, 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. OK, fair enough. If this is going to help with testing then I do not have any objections of course. > v2: Drop the full WARN_ON backtrace in favour of just a pr_warn for > the problematic case (Michal Hocko). Thanks! > 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 > Signed-off-by: Daniel Vetter > --- > mm/mmu_notifier.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c > index 5119ff846769..ccc22f21b735 100644 > --- a/mm/mmu_notifier.c > +++ b/mm/mmu_notifier.c > @@ -190,6 +190,9 @@ int __mmu_notifier_invalidate_range_start(struct mm_struct *mm, > pr_info("%pS callback failed with %d in %sblockable context.\n", > mn->ops->invalidate_range_start, _ret, > !blockable ? "non-" : ""); > + if (blockable) > + pr_warn("%pS callback failure not allowed\n", > + mn->ops->invalidate_range_start); > ret = _ret; > } > } > -- > 2.20.0.rc1 > -- Michal Hocko SUSE Labs