syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.550/11419 is trying to acquire lock:
ffff88805a100770 (sb_internal#4){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6443

but task is already holding lock:
ffff888039066bb0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
ffff888039066bb0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x237/0x4f0 mm/util.c:579

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1593
       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
       filldir+0x2b3/0x650 fs/readdir.c:289
       dir_emit include/linux/fs.h:3578 [inline]
       kernfs_fop_readdir+0x578/0x950 fs/kernfs/dir.c:2000
       iterate_dir+0x3a5/0x580 fs/readdir.c:110
       __do_sys_getdents fs/readdir.c:319 [inline]
       __se_sys_getdents+0xf1/0x270 fs/readdir.c:304
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1625
       kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:826
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1131
       sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x631/0xd10 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x12b/0x1a0 lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x116/0x2e0 fs/btrfs/sysfs.c:2604
       btrfs_quota_enable+0x282/0x2850 fs/btrfs/qgroup.c:1034
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3541
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:534 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:553
       btrfs_quota_enable+0x2c6/0x2850 fs/btrfs/qgroup.c:1063
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3541
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x192/0xd50 fs/btrfs/transaction.c:324
       start_transaction+0xbe9/0x1820 fs/btrfs/transaction.c:719
       _btrfs_ioctl_set_received_subvol+0x254/0xd20 fs/btrfs/ioctl.c:3892
       btrfs_ioctl_set_received_subvol+0x8d/0x100 fs/btrfs/ioctl.c:4006
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x171/0xd50 fs/btrfs/transaction.c:323
       start_transaction+0xbe9/0x1820 fs/btrfs/transaction.c:719
       _btrfs_ioctl_set_received_subvol+0x254/0xd20 fs/btrfs/ioctl.c:3892
       btrfs_ioctl_set_received_subvol+0x8d/0x100 fs/btrfs/ioctl.c:4006
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#4){.+.+}-{0:0}:
       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+0x106/0x350 kernel/locking/lockdep.c:5868
       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+0xaa3/0x1820 fs/btrfs/transaction.c:713
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6443
       touch_atime+0x2f8/0x6b0 fs/inode.c:2265
       file_accessed include/linux/fs.h:2264 [inline]
       btrfs_file_mmap_prepare+0x189/0x200 fs/btrfs/file.c:2051
       vfs_mmap_prepare include/linux/fs.h:2076 [inline]
       call_mmap_prepare mm/vma.c:2672 [inline]
       __mmap_region mm/vma.c:2755 [inline]
       mmap_region+0xeb9/0x2280 mm/vma.c:2857
       do_mmap+0xc2f/0x10c0 mm/mmap.c:560
       vm_mmap_pgoff+0x2cc/0x4f0 mm/util.c:581
       ksys_mmap_pgoff+0x4e8/0x720 mm/mmap.c:606
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/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:
  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 ***

2 locks held by syz.2.550/11419:
 #0: ffff888039066bb0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
 #0: ffff888039066bb0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x237/0x4f0 mm/util.c:579
 #1: ffff88805a100480 (sb_writers#27){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2264 [inline]
 #1: ffff88805a100480 (sb_writers#27){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0x189/0x200 fs/btrfs/file.c:2051

stack backtrace:
CPU: 1 UID: 0 PID: 11419 Comm: syz.2.550 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 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+0x106/0x350 kernel/locking/lockdep.c:5868
 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+0xaa3/0x1820 fs/btrfs/transaction.c:713
 btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6443
 touch_atime+0x2f8/0x6b0 fs/inode.c:2265
 file_accessed include/linux/fs.h:2264 [inline]
 btrfs_file_mmap_prepare+0x189/0x200 fs/btrfs/file.c:2051
 vfs_mmap_prepare include/linux/fs.h:2076 [inline]
 call_mmap_prepare mm/vma.c:2672 [inline]
 __mmap_region mm/vma.c:2755 [inline]
 mmap_region+0xeb9/0x2280 mm/vma.c:2857
 do_mmap+0xc2f/0x10c0 mm/mmap.c:560
 vm_mmap_pgoff+0x2cc/0x4f0 mm/util.c:581
 ksys_mmap_pgoff+0x4e8/0x720 mm/mmap.c:606
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb2e76acdd9
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:00007fb2e58e5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007fb2e7926090 RCX: 00007fb2e76acdd9
RDX: 0000000000000001 RSI: 0000000000400000 RDI: 0000200000000000
RBP: 00007fb2e7742d69 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000010012 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb2e7926128 R14: 00007fb2e7926090 R15: 00007ffc5b26d628
 </TASK>