From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id 1562C8E0001 for ; Mon, 10 Dec 2018 08:28:02 -0500 (EST) Received: by mail-ed1-f69.google.com with SMTP id v4so5182736edm.18 for ; Mon, 10 Dec 2018 05:28:02 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id a17-v6si276553ejs.24.2018.12.10.05.28.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Dec 2018 05:28:00 -0800 (PST) Date: Mon, 10 Dec 2018 14:27:59 +0100 From: Michal Hocko 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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 K�nig" > Cc: David Rientjes > Cc: Daniel Vetter > Cc: "J�r�me 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