======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.6.4060/24905 is trying to acquire lock:
ffff88807fa32650 (sb_internal#4){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6465

but task is already holding lock:
ffff888076cae540 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:562 [inline]
ffff888076cae540 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dd/0x4e0 mm/util.c:579

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0x50/0x3b0 kernel/locking/rwsem.c:1599
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:609
       get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
       lock_mm_and_find_vma+0x2d6/0x340 mm/mmap_lock.c:501
       do_user_addr_fault+0x343/0x1340 arch/x86/mm/fault.c:1366
       handle_page_fault arch/x86/mm/fault.c:1483 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
       stac arch/x86/include/asm/smap.h:-1 [inline]
       filldir64+0x29e/0x620 fs/readdir.c:370
       dir_emit include/linux/fs.h:3610 [inline]
       kernfs_fop_readdir+0x580/0x960 fs/kernfs/dir.c:1999
       iterate_dir+0x3db/0x880 fs/readdir.c:114
       __do_sys_getdents64 fs/readdir.c:404 [inline]
       __se_sys_getdents64+0xf1/0x280 fs/readdir.c:389
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x96/0x200 kernel/locking/rwsem.c:1631
       kernfs_add_one+0x41/0x6f0 fs/kernfs/dir.c:825
       kernfs_create_dir_ns+0x1a1/0x230 fs/kernfs/dir.c:1130
       sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x622/0xcd0 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+0x272/0x700 fs/btrfs/sysfs.c:1866
       btrfs_create_pending_block_groups+0xd4d/0x15e0 fs/btrfs/block-group.c:2966
       __btrfs_end_transaction+0x140/0x640 fs/btrfs/transaction.c:1102
       btrfs_inc_block_group_ro+0x64b/0x7d0 fs/btrfs/block-group.c:3249
       btrfs_relocate_block_group+0x285/0xaf0 fs/btrfs/relocation.c:5501
       btrfs_relocate_chunk+0x114/0x810 fs/btrfs/volumes.c:3729
       __btrfs_balance+0x1b5f/0x29d0 fs/btrfs/volumes.c:4668
       btrfs_balance+0xaa6/0x1180 fs/btrfs/volumes.c:5055
       btrfs_ioctl_balance+0x3da/0x640 fs/btrfs/ioctl.c:3494
       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:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x18a/0xd40 fs/btrfs/transaction.c:324
       start_transaction+0x6ed/0x17d0 fs/btrfs/transaction.c:730
       btrfs_rebuild_free_space_tree+0xbb/0x4f0 fs/btrfs/free-space-tree.c:1345
       btrfs_start_pre_rw_mount+0x15b8/0x2030 fs/btrfs/disk-io.c:3086
       open_ctree+0x2de0/0x4190 fs/btrfs/disk-io.c:3767
       btrfs_fill_super fs/btrfs/super.c:974 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1969 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2112 [inline]
       btrfs_get_tree+0x1084/0x1980 fs/btrfs/super.c:2146
       vfs_get_tree+0x92/0x2a0 fs/super.c:1932
       fc_mount fs/namespace.c:1278 [inline]
       do_new_mount_fc fs/namespace.c:3885 [inline]
       do_new_mount+0x325/0xb00 fs/namespace.c:3961
       do_mount fs/namespace.c:4325 [inline]
       __do_sys_mount fs/namespace.c:4543 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4520
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x169/0xd40 fs/btrfs/transaction.c:323
       start_transaction+0x6ed/0x17d0 fs/btrfs/transaction.c:730
       btrfs_rebuild_free_space_tree+0xbb/0x4f0 fs/btrfs/free-space-tree.c:1345
       btrfs_start_pre_rw_mount+0x15b8/0x2030 fs/btrfs/disk-io.c:3086
       open_ctree+0x2de0/0x4190 fs/btrfs/disk-io.c:3767
       btrfs_fill_super fs/btrfs/super.c:974 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1969 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2112 [inline]
       btrfs_get_tree+0x1084/0x1980 fs/btrfs/super.c:2146
       vfs_get_tree+0x92/0x2a0 fs/super.c:1932
       fc_mount fs/namespace.c:1278 [inline]
       do_new_mount_fc fs/namespace.c:3885 [inline]
       do_new_mount+0x325/0xb00 fs/namespace.c:3961
       do_mount fs/namespace.c:4325 [inline]
       __do_sys_mount fs/namespace.c:4543 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4520
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#4){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
       __sb_start_write include/linux/fs/super.h:19 [inline]
       sb_start_intwrite include/linux/fs/super.h:177 [inline]
       start_transaction+0x575/0x17d0 fs/btrfs/transaction.c:724
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6465
       touch_atime+0x2f8/0x670 fs/inode.c:2325
       file_accessed include/linux/fs.h:2279 [inline]
       btrfs_file_mmap_prepare+0x172/0x1f0 fs/btrfs/file.c:2003
       vfs_mmap_prepare include/linux/fs.h:2071 [inline]
       call_mmap_prepare mm/vma.c:2799 [inline]
       __mmap_region mm/vma.c:2888 [inline]
       mmap_region+0xe94/0x25b0 mm/vma.c:2989
       do_mmap+0xe0a/0x1300 mm/mmap.c:573
       vm_mmap_pgoff+0x272/0x4e0 mm/util.c:581
       ksys_mmap_pgoff+0x4dc/0x760 mm/mmap.c:619
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  sb_internal#4 --> &root->kernfs_rwsem --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_lock);
                               lock(&root->kernfs_rwsem);
                               lock(&mm->mmap_lock);
  rlock(sb_internal#4);

 *** DEADLOCK ***

locks held by syz.6.4060/24905: 2, last CPU#0:
 #0: ffff888076cae540 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:562 [inline]
 #0: ffff888076cae540 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dd/0x4e0 mm/util.c:579
 #1: ffff88807fa32460 (sb_writers#25){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2279 [inline]
 #1: ffff88807fa32460 (sb_writers#25){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0x172/0x1f0 fs/btrfs/file.c:2003

stack backtrace:
CPU: 0 UID: 0 PID: 24905 Comm: syz.6.4060 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
 percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
 __sb_start_write include/linux/fs/super.h:19 [inline]
 sb_start_intwrite include/linux/fs/super.h:177 [inline]
 start_transaction+0x575/0x17d0 fs/btrfs/transaction.c:724
 btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6465
 touch_atime+0x2f8/0x670 fs/inode.c:2325
 file_accessed include/linux/fs.h:2279 [inline]
 btrfs_file_mmap_prepare+0x172/0x1f0 fs/btrfs/file.c:2003
 vfs_mmap_prepare include/linux/fs.h:2071 [inline]
 call_mmap_prepare mm/vma.c:2799 [inline]
 __mmap_region mm/vma.c:2888 [inline]
 mmap_region+0xe94/0x25b0 mm/vma.c:2989
 do_mmap+0xe0a/0x1300 mm/mmap.c:573
 vm_mmap_pgoff+0x272/0x4e0 mm/util.c:581
 ksys_mmap_pgoff+0x4dc/0x760 mm/mmap.c:619
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f34a279e559
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:00007f34a35c1028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f34a2a26090 RCX: 00007f34a279e559
RDX: 0000000000000002 RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007f34a28358b0 R08: 0000000000000004 R09: 0000000000000000
R10: 0000000000028011 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f34a2a26128 R14: 00007f34a2a26090 R15: 00007ffcba98c7b8
 </TASK>