Re: [PATCH] mm: Track mmu notifiers in fs_reclaim_acquire/release

[Daniel Vetter <daniel.vetter@ffwll.ch>]

On Sun, Jun 21, 2020 at 7:42 PM Qian Cai <cai@lca.pw> 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) <thomas_os@shipmail.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Jason Gunthorpe <jgg@mellanox.com>
> > Cc: linux-mm@kvack.org
> > Cc: linux-rdma@vger.kernel.org
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>
> 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).

Thanks, Daniel


>
> [  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
> xfs_setattr_nonsize at fs/xfs/xfs_iops.c:716
> [  190.987331][  T369]        xfs_vn_setattr+0x133/0x160
> xfs_vn_setattr at fs/xfs/xfs_iops.c:1081
> [  191.010476][  T369]        notify_change+0x6c5/0xba1
> notify_change at fs/attr.c:336
> [  191.033317][  T369]        chmod_common+0x19b/0x390
> [  191.055770][  T369]        ksys_fchmod+0x28/0x60
> [  191.077957][  T369]        __x64_sys_fchmod+0x4e/0x70
> [  191.102767][  T369]        do_syscall_64+0x5f/0x310
> [  191.125090][  T369]        entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [  191.153749][  T369]
> [  191.153749][  T369] -> #0 (&xfs_nondir_ilock_class){++++}-{3:3}:
> [  191.191267][  T369]        __lock_acquire+0x2efc/0x4da0
> [  191.215974][  T369]        lock_acquire+0x1ac/0xaf0
> [  191.238953][  T369]        down_write_nested+0x92/0x150
> [  191.262955][  T369]        xfs_reclaim_inode+0xdf/0x860
> [  191.287149][  T369]        xfs_reclaim_inodes_ag+0x505/0xb00
> [  191.313291][  T369]        xfs_reclaim_inodes_nr+0x93/0xd0
> [  191.338357][  T369]        super_cache_scan+0x2fd/0x430
> [  191.362354][  T369]        do_shrink_slab+0x317/0x990
> [  191.385341][  T369]        shrink_slab+0x3a8/0x4b0
> [  191.407214][  T369]        shrink_node+0x49c/0x17b0
> [  191.429841][  T369]        balance_pgdat+0x59c/0xed0
> [  191.455041][  T369]        kswapd+0x5a4/0xc40
> [  191.477524][  T369]        kthread+0x358/0x420
> [  191.499285][  T369]        ret_from_fork+0x22/0x30
> [  191.521107][  T369]
> [  191.521107][  T369] other info that might help us debug this:
> [  191.521107][  T369]
> [  191.567490][  T369]  Possible unsafe locking scenario:
> [  191.567490][  T369]
> [  191.600947][  T369]        CPU0                    CPU1
> [  191.624808][  T369]        ----                    ----
> [  191.649236][  T369]   lock(fs_reclaim);
> [  191.667607][  T369]                                lock(&xfs_nondir_ilock_class);
> [  191.702096][  T369]                                lock(fs_reclaim);
> [  191.731243][  T369]   lock(&xfs_nondir_ilock_class);
> [  191.754025][  T369]
> [  191.754025][  T369]  *** DEADLOCK ***
> [  191.754025][  T369]
> [  191.791126][  T369] 4 locks held by kswapd3/369:
> [  191.812198][  T369]  #0: ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30
> [  191.854319][  T369]  #1: ffffffffb5074c50 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x219/0x4b0
> [  191.896043][  T369]  #2: ffff8890279b40e0 (&type->s_umount_key#27){++++}-{3:3}, at: trylock_super+0x11/0xb0
> [  191.940538][  T369]  #3: ffff889027a73a28 (&pag->pag_ici_reclaim_lock){+.+.}-{3:3}, at: xfs_reclaim_inodes_ag+0x135/0xb00
> [  191.995314][  T369]
> [  191.995314][  T369] stack backtrace:
> [  192.022934][  T369] CPU: 42 PID: 369 Comm: kswapd3 Not tainted 5.8.0-rc1-next-20200621 #1
> [  192.060546][  T369] Hardware name: HP ProLiant BL660c Gen9, BIOS I38 10/17/2018
> [  192.094518][  T369] Call Trace:
> [  192.109005][  T369]  dump_stack+0x9d/0xe0
> [  192.127468][  T369]  check_noncircular+0x347/0x400
> [  192.149526][  T369]  ? print_circular_bug+0x360/0x360
> [  192.172584][  T369]  ? freezing_slow_path.cold.2+0x2a/0x2a
> [  192.197251][  T369]  __lock_acquire+0x2efc/0x4da0
> [  192.218737][  T369]  ? lockdep_hardirqs_on_prepare+0x550/0x550
> [  192.246736][  T369]  ? __lock_acquire+0x3541/0x4da0
> [  192.269673][  T369]  lock_acquire+0x1ac/0xaf0
> [  192.290192][  T369]  ? xfs_reclaim_inode+0xdf/0x860
> [  192.313158][  T369]  ? rcu_read_unlock+0x50/0x50
> [  192.335057][  T369]  down_write_nested+0x92/0x150
> [  192.358409][  T369]  ? xfs_reclaim_inode+0xdf/0x860
> [  192.380890][  T369]  ? rwsem_down_write_slowpath+0xf50/0xf50
> [  192.406891][  T369]  ? find_held_lock+0x33/0x1c0
> [  192.427925][  T369]  ? xfs_ilock+0x2ef/0x370
> [  192.447496][  T369]  ? xfs_reclaim_inode+0xdf/0x860
> [  192.472315][  T369]  xfs_reclaim_inode+0xdf/0x860
> [  192.496649][  T369]  ? xfs_inode_clear_reclaim_tag+0xa0/0xa0
> [  192.524188][  T369]  ? do_raw_spin_unlock+0x4f/0x250
> [  192.546852][  T369]  xfs_reclaim_inodes_ag+0x505/0xb00
> [  192.570473][  T369]  ? xfs_reclaim_inode+0x860/0x860
> [  192.592692][  T369]  ? mark_held_locks+0xb0/0x110
> [  192.614287][  T369]  ? lockdep_hardirqs_on_prepare+0x38c/0x550
> [  192.640800][  T369]  ? _raw_spin_unlock_irqrestore+0x39/0x40
> [  192.666695][  T369]  ? try_to_wake_up+0xcf/0xf40
> [  192.688265][  T369]  ? migrate_swap_stop+0xc10/0xc10
> [  192.711966][  T369]  ? do_raw_spin_unlock+0x4f/0x250
> [  192.735032][  T369]  xfs_reclaim_inodes_nr+0x93/0xd0
> xfs_reclaim_inodes_nr at fs/xfs/xfs_icache.c:1399
> [  192.757674][  T369]  ? xfs_reclaim_inodes+0x90/0x90
> [  192.780028][  T369]  ? list_lru_count_one+0x177/0x300
> [  192.803010][  T369]  super_cache_scan+0x2fd/0x430
> super_cache_scan at fs/super.c:115
> [  192.824491][  T369]  do_shrink_slab+0x317/0x990
> do_shrink_slab at mm/vmscan.c:514
> [  192.845160][  T369]  shrink_slab+0x3a8/0x4b0
> shrink_slab_memcg at mm/vmscan.c:584
> (inlined by) shrink_slab at mm/vmscan.c:662
> [  192.864722][  T369]  ? do_shrink_slab+0x990/0x990
> [  192.886137][  T369]  ? rcu_is_watching+0x2c/0x80
> [  192.907289][  T369]  ? mem_cgroup_protected+0x228/0x470
> [  192.931166][  T369]  ? vmpressure+0x25/0x290
> [  192.950595][  T369]  shrink_node+0x49c/0x17b0
> [  192.972332][  T369]  balance_pgdat+0x59c/0xed0
> kswapd_shrink_node at mm/vmscan.c:3521
> (inlined by) balance_pgdat at mm/vmscan.c:3670
> [  192.994918][  T369]  ? __node_reclaim+0x950/0x950
> [  193.018625][  T369]  ? lockdep_hardirqs_on_prepare+0x38c/0x550
> [  193.046566][  T369]  ? _raw_spin_unlock_irq+0x1f/0x30
> [  193.070214][  T369]  ? _raw_spin_unlock_irq+0x1f/0x30
> [  193.093176][  T369]  ? finish_task_switch+0x129/0x650
> [  193.116225][  T369]  ? finish_task_switch+0xf2/0x650
> [  193.138809][  T369]  ? rcu_read_lock_bh_held+0xc0/0xc0
> [  193.163323][  T369]  kswapd+0x5a4/0xc40
> [  193.182690][  T369]  ? __kthread_parkme+0x4d/0x1a0
> [  193.204660][  T369]  ? balance_pgdat+0xed0/0xed0
> [  193.225776][  T369]  ? _raw_spin_unlock_irqrestore+0x39/0x40
> [  193.252306][  T369]  ? finish_wait+0x270/0x270
> [  193.272473][  T369]  ? __kthread_parkme+0x4d/0x1a0
> [  193.294476][  T369]  ? __kthread_parkme+0xcc/0x1a0
> [  193.316704][  T369]  ? balance_pgdat+0xed0/0xed0
> [  193.337808][  T369]  kthread+0x358/0x420
> [  193.355666][  T369]  ? kthread_create_worker_on_cpu+0xc0/0xc0
> [  193.381884][  T369]  ret_from_fork+0x22/0x30
>
> > ---
> > This is part of a gpu lockdep annotation series simply because it
> > really helps to catch issues where gpu subsystem locks and primitives
> > can deadlock with themselves through allocations and mmu notifiers.
> > But aside from that motivation it should be completely free-standing,
> > and can land through -mm/-rdma/-hmm or any other tree really whenever.
> > -Daniel
> > ---
> >  mm/mmu_notifier.c |  7 -------
> >  mm/page_alloc.c   | 25 ++++++++++++++++---------
> >  2 files changed, 16 insertions(+), 16 deletions(-)
> >
> > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> > index 06852b896fa6..5d578b9122f8 100644
> > --- a/mm/mmu_notifier.c
> > +++ b/mm/mmu_notifier.c
> > @@ -612,13 +612,6 @@ int __mmu_notifier_register(struct mmu_notifier *subscription,
> >       lockdep_assert_held_write(&mm->mmap_sem);
> >       BUG_ON(atomic_read(&mm->mm_users) <= 0);
> >
> > -     if (IS_ENABLED(CONFIG_LOCKDEP)) {
> > -             fs_reclaim_acquire(GFP_KERNEL);
> > -             lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
> > -             lock_map_release(&__mmu_notifier_invalidate_range_start_map);
> > -             fs_reclaim_release(GFP_KERNEL);
> > -     }
> > -
> >       if (!mm->notifier_subscriptions) {
> >               /*
> >                * kmalloc cannot be called under mm_take_all_locks(), but we
> > 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 <trace/events/oom.h>
> >  #include <linux/prefetch.h>
> >  #include <linux/mm_inline.h>
> > +#include <linux/mmu_notifier.h>
> >  #include <linux/migrate.h>
> >  #include <linux/hugetlb.h>
> >  #include <linux/sched/rt.h>
> > @@ -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);
> >
> > @@ -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();
> > +
> > +#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);
> >
> >  void fs_reclaim_release(gfp_t gfp_mask)
> >  {
> > -     if (__need_fs_reclaim(gfp_mask))
> > -             __fs_reclaim_release();
> > +     if (__need_reclaim(gfp_mask)) {
> > +             if (gfp_mask & __GFP_FS)
> > +                     __fs_reclaim_release();
> > +     }
> >  }
> >  EXPORT_SYMBOL_GPL(fs_reclaim_release);
> >  #endif
> > --
> > 2.26.2
> >
> >



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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