syzbot

======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc3-syzkaller-00044-g7595b66ae9de #0 Not tainted
------------------------------------------------------
syz.1.79/6645 is trying to acquire lock:
ffff88801ab98618 (sb_internal#3){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6225

but task is already holding lock:
ffff888072232160 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:374 [inline]
ffff888072232160 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1bd/0x4c0 mm/util.c:577

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&mm->mmap_lock){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_read_killable+0x50/0x350 kernel/locking/rwsem.c:1547
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:421
       get_mmap_lock_carefully mm/mmap_lock.c:197 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:248
       do_user_addr_fault+0x331/0x1390 arch/x86/mm/fault.c:1359
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x76/0xf0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
       filldir64+0x2c7/0x690 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3919 [inline]
       kernfs_fop_readdir+0x537/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x5af/0x770 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1577
       kernfs_add_one+0x41/0x520 fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1093
       sysfs_create_dir_ns+0x123/0x280 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x59f/0xb40 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x125/0x190 lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x111/0x2b0 fs/btrfs/sysfs.c:2635
       btrfs_quota_enable+0x278/0x1d50 fs/btrfs/qgroup.c:1030
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3673
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x182/0xe80 kernel/locking/mutex.c:747
       btrfs_quota_enable+0x2be/0x1d50 fs/btrfs/qgroup.c:1059
       btrfs_ioctl_quota_ctl+0x183/0x1c0 fs/btrfs/ioctl.c:3673
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       join_transaction+0x1a4/0xd70 fs/btrfs/transaction.c:321
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6225
       inode_update_time fs/inode.c:2076 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2149
       file_accessed include/linux/fs.h:2652 [inline]
       iterate_dir+0x64e/0x770 fs/readdir.c:111
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       join_transaction+0x182/0xd70 fs/btrfs/transaction.c:320
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6225
       inode_update_time fs/inode.c:2076 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2149
       file_accessed include/linux/fs.h:2652 [inline]
       iterate_dir+0x64e/0x770 fs/readdir.c:111
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64+0xe4/0x260 fs/readdir.c:396
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#3){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
       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.h:1795 [inline]
       sb_start_intwrite include/linux/fs.h:1978 [inline]
       start_transaction+0x56e/0x1620 fs/btrfs/transaction.c:699
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6225
       inode_update_time fs/inode.c:2076 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2149
       file_accessed include/linux/fs.h:2652 [inline]
       btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:1988
       call_mmap include/linux/fs.h:2286 [inline]
       mmap_file mm/internal.h:167 [inline]
       __mmap_new_file_vma mm/vma.c:2405 [inline]
       __mmap_new_vma mm/vma.c:2467 [inline]
       __mmap_region mm/vma.c:2622 [inline]
       mmap_region+0x127a/0x1f30 mm/vma.c:2692
       do_mmap+0xc45/0x10d0 mm/mmap.c:561
       vm_mmap_pgoff+0x31b/0x4c0 mm/util.c:579
       ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:607
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 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#3 --> &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#3);

 *** DEADLOCK ***

2 locks held by syz.1.79/6645:
 #0: ffff888072232160 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:374 [inline]
 #0: ffff888072232160 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1bd/0x4c0 mm/util.c:577
 #1: ffff88801ab98428 (sb_writers#20){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2652 [inline]
 #1: ffff88801ab98428 (sb_writers#20){.+.+}-{0:0}, at: btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:1988

stack backtrace:
CPU: 0 UID: 0 PID: 6645 Comm: syz.1.79 Not tainted 6.16.0-rc3-syzkaller-00044-g7595b66ae9de #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2046
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3911
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5240
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5871
 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.h:1795 [inline]
 sb_start_intwrite include/linux/fs.h:1978 [inline]
 start_transaction+0x56e/0x1620 fs/btrfs/transaction.c:699
 btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6225
 inode_update_time fs/inode.c:2076 [inline]
 touch_atime+0x2f9/0x6d0 fs/inode.c:2149
 file_accessed include/linux/fs.h:2652 [inline]
 btrfs_file_mmap+0xbb/0x120 fs/btrfs/file.c:1988
 call_mmap include/linux/fs.h:2286 [inline]
 mmap_file mm/internal.h:167 [inline]
 __mmap_new_file_vma mm/vma.c:2405 [inline]
 __mmap_new_vma mm/vma.c:2467 [inline]
 __mmap_region mm/vma.c:2622 [inline]
 mmap_region+0x127a/0x1f30 mm/vma.c:2692
 do_mmap+0xc45/0x10d0 mm/mmap.c:561
 vm_mmap_pgoff+0x31b/0x4c0 mm/util.c:579
 ksys_mmap_pgoff+0x51f/0x760 mm/mmap.c:607
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0ad638e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0ad713b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f0ad65b5fa0 RCX: 00007f0ad638e929
RDX: 0000000000000001 RSI: 0000000000004000 RDI: 0000200000000000
RBP: 00007f0ad6410b39 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000010012 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f0ad65b5fa0 R15: 00007ffcd574fef8
 </TASK>