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=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 59ACCC433E0 for ; Sun, 21 Jun 2020 20:01:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CE6724182 for ; Sun, 21 Jun 2020 20:01:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="byvZO+Rl" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730692AbgFUUBJ (ORCPT ); Sun, 21 Jun 2020 16:01:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55798 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730682AbgFUUBI (ORCPT ); Sun, 21 Jun 2020 16:01:08 -0400 Received: from mail-wr1-x443.google.com (mail-wr1-x443.google.com [IPv6:2a00:1450:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 19E7DC061796 for ; Sun, 21 Jun 2020 13:01:08 -0700 (PDT) Received: by mail-wr1-x443.google.com with SMTP id q5so2209021wru.6 for ; Sun, 21 Jun 2020 13:01:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=fEpisrHVuvECE9QkwBWX7rZQTVSunxWmuYR8YMHiI7w=; b=byvZO+Rl76mwx+UB97zJe2wRVGFXsyHVh1g6yyCSGTEbtPMHZ6PekdjrhFTPms5iT9 O5rQ60hDjYeFOE9E8+8Cd8jsH0OhxkGsnzwpY9RdGnAfzvdfwVITBGSoqEc++ubhg1HK yNXCwFIntsKcaqylggT66AAeH7oBzRhBsED64= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :content-transfer-encoding:in-reply-to; bh=fEpisrHVuvECE9QkwBWX7rZQTVSunxWmuYR8YMHiI7w=; b=IxNm4R+bJJiInC/mOmM8fvAG/innrShkuwAU/9WPRG1e3Ye4AY/DyV01co6eC02kog XEIYGEVWd4pmB1nIoTU9eNW3Mh8EOw3ASV1DVC/00ruIwKrLVlONnxBACH85k0/nTaX+ sj9RIz1L3gqBaO3IkcVafdIQ46dbqv9KxU9Am5x87aON9V5ZHP0Ko0r5vm9rornQgmJp uNnrHbVM3JqjHaK3dQVEeDvUd/l862S4JGSrGv6KedfH8zmOwEYbIdIF/cetjWV7Ik/2 kzJqr69jZ//vu13nC3zuMBbG0CjY9vzhG054KW4cHcZT4lJtYipl67v5GGxA8vWeq07x oOiw== X-Gm-Message-State: AOAM532Ye3zJlpaL5qCxJ05cBL1uvZTosdVeG9VnojhyfaW29rPzUn8M HQKXq/WM6l/99If5AhGUpIbPeQ== X-Google-Smtp-Source: ABdhPJxsRdQgv4E6GNxYz9Nhgg1RI6byFsAnQ/h3xQ/Wq/o2gy4VUYHPLMtLpYgEyS1HiUHhsSp98Q== X-Received: by 2002:a5d:664a:: with SMTP id f10mr15413013wrw.300.1592769666648; Sun, 21 Jun 2020 13:01:06 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id l1sm15793401wrb.31.2020.06.21.13.01.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 21 Jun 2020 13:01:05 -0700 (PDT) Date: Sun, 21 Jun 2020 22:01:03 +0200 From: Daniel Vetter To: Qian Cai Cc: Intel Graphics Development , DRI Development , LKML , amd-gfx list , Thomas =?iso-8859-1?Q?Hellstr=F6m?= , Andrew Morton , Jason Gunthorpe , Linux MM , linux-rdma , Maarten Lankhorst , Christian =?iso-8859-1?Q?K=F6nig?= , Daniel Vetter , linux-xfs@vger.kernel.org Subject: Re: [PATCH] mm: Track mmu notifiers in fs_reclaim_acquire/release Message-ID: <20200621200103.GV20149@phenom.ffwll.local> Mail-Followup-To: Qian Cai , Intel Graphics Development , DRI Development , LKML , amd-gfx list , Thomas =?iso-8859-1?Q?Hellstr=F6m?= , Andrew Morton , Jason Gunthorpe , Linux MM , linux-rdma , Maarten Lankhorst , Christian =?iso-8859-1?Q?K=F6nig?= , Daniel Vetter , linux-xfs@vger.kernel.org References: <20200604081224.863494-2-daniel.vetter@ffwll.ch> <20200610194101.1668038-1-daniel.vetter@ffwll.ch> <20200621174205.GB1398@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Operating-System: Linux phenom 5.6.0-1-amd64 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jun 21, 2020 at 08:07:08PM +0200, Daniel Vetter wrote: > On Sun, Jun 21, 2020 at 7:42 PM Qian Cai wrote: > > > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > > fs_reclaim_acquire/release nicely catch recursion issues when > > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > > to use to keep the excessive caches in check). For mmu notifier > > > recursions we do have lockdep annotations since 23b68395c7c7 > > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > > > But these only fire if a path actually results in some pte > > > invalidation - for most small allocations that's very rarely the case. > > > The other trouble is that pte invalidation can happen any time when > > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > > recursion. > > > > > > I was pondering whether we should just do the general annotation, but > > > there's always the risk for false positives. Plus I'm assuming that > > > the core fs and io code is a lot better reviewed and tested than > > > random mmu notifier code in drivers. Hence why I decide to only > > > annotate for that specific case. > > > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > > still need to explicit pull in the mmu notifier map - there's a lot > > > more places that do pte invalidation than just direct reclaim, these > > > two contexts arent the same. > > > > > > Note that the mmu notifiers needing their own independent lockdep map > > > is also the reason we can't hold them from fs_reclaim_acquire to > > > fs_reclaim_release - it would nest with the acquistion in the pte > > > invalidation code, causing a lockdep splat. And we can't remove the > > > annotations from pte invalidation and all the other places since > > > they're called from many other places than page reclaim. Hence we can > > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > > strictly more powerful. > > > > > > v2: Review from Thomas Hellstrom: > > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > > but it didn't blow up because I inverted it immediately > > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > > > Cc: Thomas Hellström (Intel) > > > Cc: Andrew Morton > > > Cc: Jason Gunthorpe > > > Cc: linux-mm@kvack.org > > > Cc: linux-rdma@vger.kernel.org > > > Cc: Maarten Lankhorst > > > Cc: Christian König > > > Signed-off-by: Daniel Vetter > > > > Replying the right patch here... > > > > Reverting this commit [1] fixed the lockdep warning below while applying > > some memory pressure. > > > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") > > Hm, then I'm confused because > - there's not mmut notifier lockdep map in the splat at a.. > - the patch is supposed to not change anything for fs_reclaim (but the > interim version got that wrong) > - looking at the paths it's kmalloc vs kswapd, both places I totally > expect fs_reflaim to be used. > > But you're claiming reverting this prevents the lockdep splat. If > that's right, then my reasoning above is broken somewhere. Someone > less blind than me having an idea? > > Aside this is the first email I've typed, until I realized the first > report was against the broken patch and that looked like a much more > reasonable explanation (but didn't quite match up with the code > paths). Below diff should undo the functional change in my patch. Can you pls test whether the lockdep splat is really gone with that? Might need a lot of testing and memory pressure to be sure, since all these reclaim paths aren't very deterministic. -Daniel --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d807587c9ae6..27ea763c6155 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4191,11 +4191,6 @@ void fs_reclaim_acquire(gfp_t gfp_mask) if (gfp_mask & __GFP_FS) __fs_reclaim_acquire(); -#ifdef CONFIG_MMU_NOTIFIER - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); - lock_map_release(&__mmu_notifier_invalidate_range_start_map); -#endif - } } EXPORT_SYMBOL_GPL(fs_reclaim_acquire); -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch