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, URIBL_BLOCKED,USER_AGENT_SANE_1 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 8A2B7C433DF for ; Tue, 23 Jun 2020 23:02:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6A47E20780 for ; Tue, 23 Jun 2020 23:02:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388370AbgFWXCg (ORCPT ); Tue, 23 Jun 2020 19:02:36 -0400 Received: from mail108.syd.optusnet.com.au ([211.29.132.59]:55558 "EHLO mail108.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387769AbgFWXCf (ORCPT ); Tue, 23 Jun 2020 19:02:35 -0400 Received: from dread.disaster.area (pa49-180-124-177.pa.nsw.optusnet.com.au [49.180.124.177]) by mail108.syd.optusnet.com.au (Postfix) with ESMTPS id 7EAF41A8342; Wed, 24 Jun 2020 08:31:36 +1000 (AEST) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1jnrS3-0000sh-12; Wed, 24 Jun 2020 08:31:35 +1000 Date: Wed, 24 Jun 2020 08:31:35 +1000 From: Dave Chinner To: Qian Cai Cc: Daniel Vetter , Intel Graphics Development , DRI Development , LKML , amd-gfx@lists.freedesktop.org, Thomas =?iso-8859-1?Q?Hellstr=F6m?= , Andrew Morton , Jason Gunthorpe , linux-mm@kvack.org, linux-rdma@vger.kernel.org, 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: <20200623223134.GC2005@dread.disaster.area> 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: <20200621174205.GB1398@lca.pw> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=k3aV/LVJup6ZGWgigO6cSA==:117 a=k3aV/LVJup6ZGWgigO6cSA==:17 a=8nJEP1OIZ-IA:10 a=nTHF0DUjJn0A:10 a=WwJGiR1sAAAA:8 a=Z4Rwk6OoAAAA:8 a=CbDCq_QkAAAA:8 a=37rDS-QxAAAA:8 a=VwQbUJbxAAAA:8 a=QyXUC8HyAAAA:8 a=zd2uoN0lAAAA:8 a=7-415B0cAAAA:8 a=YFjDoilscawXd35iVQoA:9 a=wPNLvfGTeEIA:10 a=Ke8zcFn7cQlxtk25vvl_:22 a=HkZW87K1Qel5hWWM3VKY:22 a=1qrBK16LubpBFNPVNq2M:22 a=k1Nq6YrhK2t884LQW06G:22 a=AjGcO6oz07-iQ99wixmX:22 a=biEYGPWJfzWAr4FL6Ov7:22 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 01:42:05PM -0400, 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") > > [ 190.455003][ T369] WARNING: possible circular locking dependency detected > [ 190.487291][ T369] 5.8.0-rc1-next-20200621 #1 Not tainted > [ 190.512363][ T369] ------------------------------------------------------ > [ 190.543354][ T369] kswapd3/369 is trying to acquire lock: > [ 190.568523][ T369] ffff889fcf694528 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_reclaim_inode+0xdf/0x860 > spin_lock at include/linux/spinlock.h:353 > (inlined by) xfs_iflags_test_and_set at fs/xfs/xfs_inode.h:166 > (inlined by) xfs_iflock_nowait at fs/xfs/xfs_inode.h:249 > (inlined by) xfs_reclaim_inode at fs/xfs/xfs_icache.c:1127 > [ 190.614359][ T369] > [ 190.614359][ T369] but task is already holding lock: > [ 190.647763][ T369] ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 > __fs_reclaim_acquire at mm/page_alloc.c:4200 > [ 190.687845][ T369] > [ 190.687845][ T369] which lock already depends on the new lock. > [ 190.687845][ T369] > [ 190.734890][ T369] > [ 190.734890][ T369] the existing dependency chain (in reverse order) is: > [ 190.775991][ T369] > [ 190.775991][ T369] -> #1 (fs_reclaim){+.+.}-{0:0}: > [ 190.808150][ T369] fs_reclaim_acquire+0x77/0x80 > [ 190.832152][ T369] slab_pre_alloc_hook.constprop.52+0x20/0x120 > slab_pre_alloc_hook at mm/slab.h:507 > [ 190.862173][ T369] kmem_cache_alloc+0x43/0x2a0 > [ 190.885602][ T369] kmem_zone_alloc+0x113/0x3ef > kmem_zone_alloc at fs/xfs/kmem.c:129 > [ 190.908702][ T369] xfs_inode_item_init+0x1d/0xa0 > xfs_inode_item_init at fs/xfs/xfs_inode_item.c:639 > [ 190.934461][ T369] xfs_trans_ijoin+0x96/0x100 > xfs_trans_ijoin at fs/xfs/libxfs/xfs_trans_inode.c:34 > [ 190.961530][ T369] xfs_setattr_nonsize+0x1a6/0xcd0 OK, this patch has royally screwed something up if this path thinks it can enter memory reclaim. This path is inside a transaction, so it is running under PF_MEMALLOC_NOFS context, so should *never* enter memory reclaim. I'd suggest that whatever mods were made to fs_reclaim_acquire by this patch broke it's basic functionality.... > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 13cc653122b7..7536faaaa0fd 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -57,6 +57,7 @@ > > #include > > #include > > #include > > +#include > > #include > > #include > > #include > > @@ -4124,7 +4125,7 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla > > static struct lockdep_map __fs_reclaim_map = > > STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map); > > > > -static bool __need_fs_reclaim(gfp_t gfp_mask) > > +static bool __need_reclaim(gfp_t gfp_mask) > > { > > gfp_mask = current_gfp_context(gfp_mask); This is applies the per-task memory allocation context flags to the mask that is checked here. > > @@ -4136,10 +4137,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) > > if (current->flags & PF_MEMALLOC) > > return false; > > > > - /* We're only interested __GFP_FS allocations for now */ > > - if (!(gfp_mask & __GFP_FS)) > > - return false; > > - > > if (gfp_mask & __GFP_NOLOCKDEP) > > return false; > > > > @@ -4158,15 +4155,25 @@ void __fs_reclaim_release(void) > > > > void fs_reclaim_acquire(gfp_t gfp_mask) > > { > > - if (__need_fs_reclaim(gfp_mask)) > > - __fs_reclaim_acquire(); > > + if (__need_reclaim(gfp_mask)) { > > + if (gfp_mask & __GFP_FS) > > + __fs_reclaim_acquire(); .... and they have not been applied in this path. There's your breakage. For future reference, please post anything that changes NOFS allocation contexts or behaviours to linux-fsdevel, as filesystem developers need to know about proposed changes to infrastructure that is critical to the correct functioning of filesystems... Cheers, Dave. -- Dave Chinner david@fromorbit.com