Re: [syzbot] [mm?] possible deadlock in rhashtable_free_and_destroy

Michal Hocko
2026-04-27T07:00:04Z

Same issue as https://lkml.kernel.org/r/202604211323.fac1b29e-lkp@intel.com

On Tue 21-04-26 14:27:35, Shakeel Butt wrote:
> Ccing relevant folks as this seems related to recent change of moving
> simple_xattrs from rbtree to rhastable.
>
> On Tue, Apr 21, 2026 at 08:34:22AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: 8541d8f725c6 Merge tag 'mtd/for-7.1' of git://git.kernel.o..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=15380836580000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=7e54da1916e8d11f
> > dashboard link: https://syzkaller.appspot.com/bug?extid=5af806780f38a5fe691f
> > compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-8541d8f7.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/22dfea2c37c2/vmlinux-8541d8f7.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/e2f93ad68fe3/bzImage-8541d8f7.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+5af806780f38a5fe691f@syzkaller.appspotmail.com
> >
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > syzkaller #0 Tainted: G L
> > ------------------------------------------------------
> > kswapd0/108 is trying to acquire lock:
> > ffff888056f3c4e8 (&ht->mutex){+.+.}-{4:4}, at: rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154
> >
> > but task is already holding lock:
> > ffffffff8e9b0800 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xb5d/0x1ac0 mm/vmscan.c:7102
> >
> > 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:4327 [inline]
> > fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4341
> > 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:632 [inline]
> > __mutex_lock+0x1a4/0x1b10 kernel/locking/mutex.c:806
>
> The cancel_work_sync(&ht->run_work) in rhashtable_free_and_destroy() should
> avoid concurrent mutex lockers from rht_deferred_worker(). Seems like false
> positive as all rhastables share single static lockdep class for the ht->mutex.
>
> Simple fix would be to move rhashtable_rehash_alloc() to use NOFS allocation or
> we can introduce more fine grained lockdep classes for rhashtables.
>
> > rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154
> > shmem_evict_inode+0x1ae/0xc40 mm/shmem.c:1429
> > 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+0x2a1/0x490 fs/dcache.c:467
> > __dentry_kill+0x1d0/0x600 fs/dcache.c:670
> > finish_dput+0x76/0x480 fs/dcache.c:879
> > dput.part.0+0x456/0x570 fs/dcache.c:928
> > dput+0x1f/0x30 fs/dcache.c:920
> > ovl_destroy_inode+0x3e/0x190 fs/overlayfs/super.c:217
> > destroy_inode+0xcb/0x1c0 fs/inode.c:394
> > evict+0x599/0xad0 fs/inode.c:865
> > 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+0x2a1/0x490 fs/dcache.c:467
> > __dentry_kill+0x1d0/0x600 fs/dcache.c:670
> > shrink_kill fs/dcache.c:1147 [inline]
> > shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1174
> > prune_dcache_sb+0xea/0x150 fs/dcache.c:1256
> > super_cache_scan+0x328/0x550 fs/super.c:223
> > do_shrink_slab+0x416/0x1240 mm/shrinker.c:440
> > shrink_slab_memcg mm/shrinker.c:557 [inline]
> > shrink_slab+0xa7d/0x12e0 mm/shrinker.c:635
> > shrink_one+0x398/0x7f0 mm/vmscan.c:4932
> > shrink_many mm/vmscan.c:4993 [inline]
> > lru_gen_shrink_node mm/vmscan.c:5071 [inline]
> > shrink_node+0x2673/0x3dc0 mm/vmscan.c:6059
> > kswapd_shrink_node mm/vmscan.c:6913 [inline]
> > balance_pgdat+0xaaf/0x1ac0 mm/vmscan.c:7089
> > kswapd+0x557/0xb60 mm/vmscan.c:7362
> > 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 kswapd0/108:
> > #0: ffffffff8e9b0800 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xb5d/0x1ac0 mm/vmscan.c:7102
> > #1: ffff88801347c0d8 (&type->s_umount_key#76){++++}-{4:4}, at: super_trylock_shared fs/super.c:565 [inline]
> > #1: ffff88801347c0d8 (&type->s_umount_key#76){++++}-{4:4}, at: super_cache_scan+0x98/0x550 fs/super.c:198
> >
> > stack backtrace:
> > CPU: 2 UID: 0 PID: 108 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:632 [inline]
> > __mutex_lock+0x1a4/0x1b10 kernel/locking/mutex.c:806
> > rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154
> > shmem_evict_inode+0x1ae/0xc40 mm/shmem.c:1429
> > 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+0x2a1/0x490 fs/dcache.c:467
> > __dentry_kill+0x1d0/0x600 fs/dcache.c:670
> > finish_dput+0x76/0x480 fs/dcache.c:879
> > dput.part.0+0x456/0x570 fs/dcache.c:928
> > dput+0x1f/0x30 fs/dcache.c:920
> > ovl_destroy_inode+0x3e/0x190 fs/overlayfs/super.c:217
> > destroy_inode+0xcb/0x1c0 fs/inode.c:394
> > evict+0x599/0xad0 fs/inode.c:865
> > 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+0x2a1/0x490 fs/dcache.c:467
> > __dentry_kill+0x1d0/0x600 fs/dcache.c:670
> > shrink_kill fs/dcache.c:1147 [inline]
> > shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1174
> > prune_dcache_sb+0xea/0x150 fs/dcache.c:1256
> > super_cache_scan+0x328/0x550 fs/super.c:223
> > do_shrink_slab+0x416/0x1240 mm/shrinker.c:440
> > shrink_slab_memcg mm/shrinker.c:557 [inline]
> > shrink_slab+0xa7d/0x12e0 mm/shrinker.c:635
> > shrink_one+0x398/0x7f0 mm/vmscan.c:4932
> > shrink_many mm/vmscan.c:4993 [inline]
> > lru_gen_shrink_node mm/vmscan.c:5071 [inline]
> > shrink_node+0x2673/0x3dc0 mm/vmscan.c:6059
> > kswapd_shrink_node mm/vmscan.c:6913 [inline]
> > balance_pgdat+0xaaf/0x1ac0 mm/vmscan.c:7089
> > kswapd+0x557/0xb60 mm/vmscan.c:7362
> > 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>
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> >
> > If the report is already addressed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
> >
> > If you want to overwrite report's subsystems, reply with:
> > #syz set subsystems: new-subsystem
> > (See the list of subsystem names on the web dashboard)
> >
> > If the report is a duplicate of another one, reply with:
> > #syz dup: exact-subject-of-another-report
> >
> > If you want to undo deduplication, reply with:
> > #syz undup

--
Michal Hocko
SUSE Labs