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

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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@xxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-rdma@xxxxxxxxxxxxxxx
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>

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
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
> 
> 
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