Hi,

left my box unattended for a while and lockdep reported this:

| ======================================================
| WARNING: possible circular locking dependency detected
| 5.16.0-rc1+ #12 Not tainted
| ------------------------------------------------------
| kswapd1/510 is trying to acquire lock:
| ffff88800c98ac70 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_icwalk_ag+0x365/0x810
|
| but task is already holding lock:
| ffffffff82a76d60 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x4c4/0x5b0
|
| which lock already depends on the new lock.
|
|
| the existing dependency chain (in reverse order) is:
|
| -> #1 (fs_reclaim){+.+.}-{0:0}:
|        fs_reclaim_acquire+0xa1/0xd0
|        __alloc_pages+0xed/0x380
|        new_slab+0x277/0x430
|        ___slab_alloc.constprop.0+0xb6a/0xfc0
|        __slab_alloc.constprop.0+0x42/0x80
|        __kmalloc_node+0xcc/0x200
|        xfs_attr_copy_value+0x6e/0x90
|        xfs_attr_get+0xa0/0xc0
|        xfs_get_acl+0xe4/0x210
|        get_acl.part.0+0x55/0x110
|        posix_acl_xattr_get+0x6a/0x120
|        vfs_getxattr+0x172/0x1a0
|        getxattr+0xb5/0x240
|        __x64_sys_fgetxattr+0x66/0xb0
|        do_syscall_64+0x59/0x80
|        entry_SYSCALL_64_after_hwframe+0x44/0xae
|
| -> #0 (&xfs_nondir_ilock_class){++++}-{3:3}:
|        __lock_acquire+0x12cb/0x2320
|        lock_acquire+0xc9/0x2e0
|        down_write_nested+0x42/0x110
|        xfs_icwalk_ag+0x365/0x810
|        xfs_icwalk+0x38/0xa0
|        xfs_reclaim_inodes_nr+0x90/0xc0
|        super_cache_scan+0x18e/0x1f0
|        shrink_slab.constprop.0+0x1cf/0x4d0
|        shrink_node+0x1e2/0x470
|        balance_pgdat+0x26d/0x5b0
|        kswapd+0x224/0x4e0
|        kthread+0x17a/0x1a0
|        ret_from_fork+0x1f/0x30
|
| other info that might help us debug this:
|
|  Possible unsafe locking scenario:
|        CPU0                    CPU1
|        ----                    ----
|   lock(fs_reclaim);
|                                lock(&xfs_nondir_ilock_class);
|                                lock(fs_reclaim);
|   lock(&xfs_nondir_ilock_class);
|
|  *** DEADLOCK ***
|
| 3 locks held by kswapd1/510:
|  #0: ffffffff82a76d60 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x4c4/0x5b0
|  #1: ffffffff82a69d58 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab.constprop.0+0x3b/0x4d0
|  #2: ffff888553ccd0e8 (&type->s_umount_key#32){++++}-{3:3}, at: super_cache_scan+0x38/0x1f0
|
| stack backtrace:
| CPU: 12 PID: 510 Comm: kswapd1 Not tainted 5.16.0-rc1+ #12
| Hardware name: Intel Corporation S2600CP/S2600CP, BIOS SE5C600.86B.02.03.0003.041920141333 04/19/2014
| Call Trace:
|  <TASK>
|  dump_stack_lvl+0x45/0x59
|  check_noncircular+0xff/0x110
|  __lock_acquire+0x12cb/0x2320
|  lock_acquire+0xc9/0x2e0
|  ? xfs_icwalk_ag+0x365/0x810
|  ? lock_is_held_type+0xd6/0x130
|  down_write_nested+0x42/0x110
|  ? xfs_icwalk_ag+0x365/0x810
|  xfs_icwalk_ag+0x365/0x810
|  xfs_icwalk+0x38/0xa0
|  xfs_reclaim_inodes_nr+0x90/0xc0
|  super_cache_scan+0x18e/0x1f0
|  shrink_slab.constprop.0+0x1cf/0x4d0
|  shrink_node+0x1e2/0x470
|  balance_pgdat+0x26d/0x5b0
|  ? lock_is_held_type+0xd6/0x130
|  kswapd+0x224/0x4e0
|  ? wait_woken+0x90/0x90
|  ? balance_pgdat+0x5b0/0x5b0
|  kthread+0x17a/0x1a0
|  ? set_kthread_struct+0x40/0x40
|  ret_from_fork+0x1f/0x30
|  </TASK>

It appears to be related to commit
   d634525db63e9 ("xfs: replace kmem_alloc_large() with kvmalloc()")

as SLUB's new_slab() has
|     return allocate_slab(s,
|            flags & (GFP_RECLAIM_MASK | GFP_CONSTRAINT_MASK), node);

which drops the __GFP_NOLOCKDEP as used in xfs_attr_copy_value():
|     args->value = kvmalloc(valuelen, GFP_KERNEL | __GFP_NOLOCKDEP);

However I can't tell if this should happen or not I'm just pointing out
that it is.

Sebastian