====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ syz.5.1457/13048 is trying to acquire lock: ffff88802ad3b440 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601 but task is already holding lock: ffff88801bad5988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x266/0x950 fs/kernfs/dir.c:1926 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&root->kernfs_rwsem){++++}-{4:4}: down_write+0x96/0x200 kernel/locking/rwsem.c:1590 kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:813 kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1118 sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59 create_dir lib/kobject.c:73 [inline] kobject_add_internal+0x62b/0xd00 lib/kobject.c:240 kobject_add_varg lib/kobject.c:374 [inline] kobject_add+0x163/0x240 lib/kobject.c:426 btrfs_sysfs_add_block_group_type+0x243/0x6c0 fs/btrfs/sysfs.c:1866 btrfs_create_pending_block_groups+0xd77/0x1b40 fs/btrfs/block-group.c:2902 __btrfs_end_transaction+0x140/0x640 fs/btrfs/transaction.c:1080 btrfs_inc_block_group_ro+0x647/0x7c0 fs/btrfs/block-group.c:3181 btrfs_relocate_block_group+0x39e/0xbc0 fs/btrfs/relocation.c:5367 btrfs_relocate_chunk+0x115/0x820 fs/btrfs/volumes.c:3590 __btrfs_balance+0x1db0/0x2ae0 fs/btrfs/volumes.c:4501 btrfs_balance+0xafa/0x11f0 fs/btrfs/volumes.c:4888 btrfs_ioctl_balance+0x3d3/0x610 fs/btrfs/ioctl.c:3452 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #2 (btrfs_trans_num_extwriters){++++}-{0:0}: join_transaction+0x1a4/0xd60 fs/btrfs/transaction.c:323 start_transaction+0x6b9/0x1650 fs/btrfs/transaction.c:708 btrfs_rebuild_free_space_tree+0xbb/0x6e0 fs/btrfs/free-space-tree.c:1335 btrfs_start_pre_rw_mount+0x1529/0x1f20 fs/btrfs/disk-io.c:3071 open_ctree+0x2e07/0x4220 fs/btrfs/disk-io.c:3668 btrfs_fill_super fs/btrfs/super.c:981 [inline] btrfs_get_tree_super fs/btrfs/super.c:1944 [inline] btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline] btrfs_get_tree+0x1061/0x1930 fs/btrfs/super.c:2121 vfs_get_tree+0x92/0x2a0 fs/super.c:1754 fc_mount fs/namespace.c:1193 [inline] do_new_mount_fc fs/namespace.c:3763 [inline] do_new_mount+0x341/0xd30 fs/namespace.c:3839 do_mount fs/namespace.c:4172 [inline] __do_sys_mount fs/namespace.c:4361 [inline] __se_sys_mount+0x31d/0x420 fs/namespace.c:4338 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (btrfs_trans_num_writers){++++}-{0:0}: __lock_release kernel/locking/lockdep.c:5574 [inline] lock_release+0x199/0x3d0 kernel/locking/lockdep.c:5889 percpu_up_read include/linux/percpu-rwsem.h:112 [inline] __sb_end_write include/linux/fs/super.h:14 [inline] sb_end_intwrite+0x26/0x1c0 include/linux/fs/super.h:101 __btrfs_end_transaction+0x248/0x640 fs/btrfs/transaction.c:1085 btrfs_dirty_inode+0x14c/0x190 fs/btrfs/inode.c:6457 touch_atime+0x2f8/0x6b0 fs/inode.c:2271 file_accessed include/linux/fs.h:2263 [inline] btrfs_file_mmap_prepare+0x172/0x1f0 fs/btrfs/file.c:2051 vfs_mmap_prepare include/linux/fs.h:2075 [inline] call_mmap_prepare mm/vma.c:2644 [inline] __mmap_region mm/vma.c:2743 [inline] mmap_region+0xdac/0x22a0 mm/vma.c:2844 do_mmap+0xc39/0x10c0 mm/mmap.c:559 vm_mmap_pgoff+0x2c9/0x4f0 mm/util.c:581 ksys_mmap_pgoff+0x51e/0x760 mm/mmap.c:605 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (&mm->mmap_lock){++++}-{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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868 down_read_killable+0x50/0x340 kernel/locking/rwsem.c:1560 mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601 get_mmap_lock_carefully mm/mmap_lock.c:450 [inline] lock_mm_and_find_vma+0x2d7/0x340 mm/mmap_lock.c:501 do_user_addr_fault+0x330/0x1340 arch/x86/mm/fault.c:1357 handle_page_fault arch/x86/mm/fault.c:1474 [inline] exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618 user_access_begin arch/x86/include/asm/uaccess.h:-1 [inline] filldir64+0x29c/0x670 fs/readdir.c:374 dir_emit include/linux/fs.h:3566 [inline] kernfs_fop_readdir+0x575/0x950 fs/kernfs/dir.c:1943 iterate_dir+0x399/0x570 fs/readdir.c:108 __do_sys_getdents64 fs/readdir.c:412 [inline] __se_sys_getdents64+0xf1/0x280 fs/readdir.c:397 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: &mm->mmap_lock --> btrfs_trans_num_extwriters --> &root->kernfs_rwsem Possible unsafe locking scenario: CPU0 CPU1 ---- ---- rlock(&root->kernfs_rwsem); lock(btrfs_trans_num_extwriters); lock(&root->kernfs_rwsem); rlock(&mm->mmap_lock); *** DEADLOCK *** 3 locks held by syz.5.1457/13048: #0: ffff88807b3c6478 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320 fs/file.c:1261 #1: ffff888011e94bd0 (&type->i_mutex_dir_key#4){++++}-{4:4}, at: iterate_dir+0x292/0x570 fs/readdir.c:101 #2: ffff88801bad5988 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_fop_readdir+0x266/0x950 fs/kernfs/dir.c:1926 stack backtrace: CPU: 1 UID: 0 PID: 13048 Comm: syz.5.1457 Tainted: G L syzkaller #0 PREEMPT(full) Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043 check_noncircular+0x12e/0x150 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868 down_read_killable+0x50/0x340 kernel/locking/rwsem.c:1560 mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:601 get_mmap_lock_carefully mm/mmap_lock.c:450 [inline] lock_mm_and_find_vma+0x2d7/0x340 mm/mmap_lock.c:501 do_user_addr_fault+0x330/0x1340 arch/x86/mm/fault.c:1357 handle_page_fault arch/x86/mm/fault.c:1474 [inline] exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618 RIP: 0010:filldir64+0x29c/0x670 fs/readdir.c:378 Code: 7d ff 4c 89 ff 4c 89 e6 e8 71 57 7d ff 4d 39 e7 0f 82 5b 02 00 00 49 39 ef 0f 87 52 02 00 00 0f 01 cb 0f ae e8 48 8b 44 24 50 <49> 89 44 24 08 48 8b 4c 24 08 48 8b 44 24 58 48 89 01 48 8b 04 24 RSP: 0018:ffffc90004b37c40 EFLAGS: 00050283 RAX: 0000000004aede41 RBX: ffffc90004b37e38 RCX: ffff88801b398000 RDX: 0000000000000002 RSI: 0000000000000000 RDI: 0000000000000020 RBP: 00007ffffffff000 R08: 0000000000000de4 R09: 0000000000000004 R10: dffffc0000000000 R11: ffffffff82486780 R12: 0000000000000000 R13: ffffffff8c8d3dc0 R14: 0000000000000006 R15: 0000000000000020 dir_emit include/linux/fs.h:3566 [inline] kernfs_fop_readdir+0x575/0x950 fs/kernfs/dir.c:1943 iterate_dir+0x399/0x570 fs/readdir.c:108 __do_sys_getdents64 fs/readdir.c:412 [inline] __se_sys_getdents64+0xf1/0x280 fs/readdir.c:397 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f386bb9c819 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f386caea028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9 RAX: ffffffffffffffda RBX: 00007f386be15fa0 RCX: 00007f386bb9c819 RDX: 000000000000004f RSI: 0000000000000000 RDI: 0000000000000006 RBP: 00007f386bc32c91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f386be16038 R14: 00007f386be15fa0 R15: 00007fff90d4cae8 ---------------- Code disassembly (best guess): 0: 7d ff jge 0x1 2: 4c 89 ff mov %r15,%rdi 5: 4c 89 e6 mov %r12,%rsi 8: e8 71 57 7d ff call 0xff7d577e d: 4d 39 e7 cmp %r12,%r15 10: 0f 82 5b 02 00 00 jb 0x271 16: 49 39 ef cmp %rbp,%r15 19: 0f 87 52 02 00 00 ja 0x271 1f: 0f 01 cb stac 22: 0f ae e8 lfence 25: 48 8b 44 24 50 mov 0x50(%rsp),%rax * 2a: 49 89 44 24 08 mov %rax,0x8(%r12) <-- trapping instruction 2f: 48 8b 4c 24 08 mov 0x8(%rsp),%rcx 34: 48 8b 44 24 58 mov 0x58(%rsp),%rax 39: 48 89 01 mov %rax,(%rcx) 3c: 48 8b 04 24 mov (%rsp),%rax