Re: [PATCH 01/18] mm: Track mmu notifiers in fs_reclaim_acquire/release

From: Qian Cai
Date: Sun Jun 21 2020 - 13:01:12 EST

On Thu, Jun 04, 2020 at 10:12:07AM +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.
>
> 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>

Reverting this commit fixed the lockdep splat below while applying some
memory pressure,

[ 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 | 23 ++++++++++++++---------
> 2 files changed, 14 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..f8a222db4a53 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 +4155,23 @@ 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();
> +
> + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
> + lock_map_release(&__mmu_notifier_invalidate_range_start_map);
> +
> + }
> }
> 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
>
>