syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kswapd0/107 is trying to acquire lock:
ffff88802b1fd4e8 (&ht->mutex){+.+.}-{4:4}, at: rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154

but task is already holding lock:
ffffffff8e9b1800 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xb5d/0x1ac0 mm/vmscan.c:7241

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (fs_reclaim){+.+.}-{0:0}:
       __fs_reclaim_acquire mm/page_alloc.c:4325 [inline]
       fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4339
       might_alloc include/linux/sched/mm.h:317 [inline]
       slab_pre_alloc_hook mm/slub.c:4520 [inline]
       slab_alloc_node mm/slub.c:4875 [inline]
       __do_kmalloc_node mm/slub.c:5294 [inline]
       __kvmalloc_node_noprof+0xcc/0xa00 mm/slub.c:6828
       bucket_table_alloc.isra.0+0x88/0x460 lib/rhashtable.c:186
       rhashtable_rehash_alloc+0x68/0x110 lib/rhashtable.c:368
       rht_deferred_worker+0x1d9/0x1fd0 lib/rhashtable.c:429
       process_one_work+0xa0e/0x1980 kernel/workqueue.c:3302
       process_scheduled_works kernel/workqueue.c:3385 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3466
       kthread+0x370/0x450 kernel/kthread.c:436
       ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&ht->mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x1b1/0x370 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1b10 kernel/locking/mutex.c:820
       rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154
       kernfs_put.part.0+0x175/0x720 fs/kernfs/dir.c:609
       kernfs_put+0x53/0x60 fs/kernfs/dir.c:629
       evict+0x3c2/0xad0 fs/inode.c:841
       iput_final fs/inode.c:1960 [inline]
       iput.part.0+0x605/0xf50 fs/inode.c:2009
       iput+0x35/0x40 fs/inode.c:1975
       dentry_unlink_inode+0x2c0/0x4c0 fs/dcache.c:476
       __dentry_kill+0x1d0/0x690 fs/dcache.c:718
       shrink_kill fs/dcache.c:1195 [inline]
       shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1222
       prune_dcache_sb+0xea/0x150 fs/dcache.c:1304
       super_cache_scan+0x328/0x550 fs/super.c:223
       do_shrink_slab+0x416/0x1240 mm/shrinker.c:436
       shrink_slab_memcg mm/shrinker.c:553 [inline]
       shrink_slab+0xa7d/0x12e0 mm/shrinker.c:631
       shrink_one+0x398/0x7f0 mm/vmscan.c:5071
       shrink_many mm/vmscan.c:5132 [inline]
       lru_gen_shrink_node mm/vmscan.c:5210 [inline]
       shrink_node+0x2673/0x3dc0 mm/vmscan.c:6198
       kswapd_shrink_node mm/vmscan.c:7052 [inline]
       balance_pgdat+0xaaf/0x1ac0 mm/vmscan.c:7228
       kswapd+0x557/0xb60 mm/vmscan.c:7501
       kthread+0x370/0x450 kernel/kthread.c:436
       ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(fs_reclaim);
                               lock(&ht->mutex);
                               lock(fs_reclaim);
  lock(&ht->mutex);

 *** DEADLOCK ***

2 locks held by kswapd0/107:
 #0: ffffffff8e9b1800 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xb5d/0x1ac0 mm/vmscan.c:7241
 #1: ffff8880355700d8 (&type->s_umount_key#64){++++}-{4:4}, at: super_trylock_shared fs/super.c:565 [inline]
 #1: ffff8880355700d8 (&type->s_umount_key#64){++++}-{4:4}, at: super_cache_scan+0x98/0x550 fs/super.c:198

stack backtrace:
CPU: 0 UID: 0 PID: 107 Comm: kswapd0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1b1/0x370 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1b10 kernel/locking/mutex.c:820
 rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154
 kernfs_put.part.0+0x175/0x720 fs/kernfs/dir.c:609
 kernfs_put+0x53/0x60 fs/kernfs/dir.c:629
 evict+0x3c2/0xad0 fs/inode.c:841
 iput_final fs/inode.c:1960 [inline]
 iput.part.0+0x605/0xf50 fs/inode.c:2009
 iput+0x35/0x40 fs/inode.c:1975
 dentry_unlink_inode+0x2c0/0x4c0 fs/dcache.c:476
 __dentry_kill+0x1d0/0x690 fs/dcache.c:718
 shrink_kill fs/dcache.c:1195 [inline]
 shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1222
 prune_dcache_sb+0xea/0x150 fs/dcache.c:1304
 super_cache_scan+0x328/0x550 fs/super.c:223
 do_shrink_slab+0x416/0x1240 mm/shrinker.c:436
 shrink_slab_memcg mm/shrinker.c:553 [inline]
 shrink_slab+0xa7d/0x12e0 mm/shrinker.c:631
 shrink_one+0x398/0x7f0 mm/vmscan.c:5071
 shrink_many mm/vmscan.c:5132 [inline]
 lru_gen_shrink_node mm/vmscan.c:5210 [inline]
 shrink_node+0x2673/0x3dc0 mm/vmscan.c:6198
 kswapd_shrink_node mm/vmscan.c:7052 [inline]
 balance_pgdat+0xaaf/0x1ac0 mm/vmscan.c:7228
 kswapd+0x557/0xb60 mm/vmscan.c:7501
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>