syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.4.264/7405 is trying to acquire lock:
ffff8880632e4770 (sb_internal#5){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6270

but task is already holding lock:
ffff88803b503050 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:330 [inline]
ffff88803b503050 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x214/0x4d0 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}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_read_killable+0x9d/0x220 kernel/locking/rwsem.c:1560
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:377
       get_mmap_lock_carefully mm/mmap_lock.c:377 [inline]
       lock_mm_and_find_vma+0x2a8/0x300 mm/mmap_lock.c:428
       do_user_addr_fault+0x331/0x1380 arch/x86/mm/fault.c:1359
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x82/0x100 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
       filldir+0x2b6/0x6c0 fs/readdir.c:295
       dir_emit include/linux/fs.h:3986 [inline]
       kernfs_fop_readdir+0x53a/0x870 fs/kernfs/dir.c:1910
       iterate_dir+0x3a5/0x580 fs/readdir.c:108
       __do_sys_getdents fs/readdir.c:326 [inline]
       __se_sys_getdents+0xe4/0x250 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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:5868
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
       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+0x5a5/0xb50 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:2645
       btrfs_quota_enable+0x25d/0x2920 fs/btrfs/qgroup.c:1022
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3667
       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+0xfa/0xfa0 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:5868
       __mutex_lock_common kernel/locking/rtmutex_api.c:535 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:547
       btrfs_quota_enable+0x29c/0x2920 fs/btrfs/qgroup.c:1051
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3667
       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+0xfa/0xfa0 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:5868
       join_transaction+0x1a4/0xca0 fs/btrfs/transaction.c:321
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6270
       inode_update_time fs/inode.c:2117 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2190
       file_accessed include/linux/fs.h:2673 [inline]
       iterate_dir+0x44a/0x580 fs/readdir.c:111
       __do_sys_getdents fs/readdir.c:326 [inline]
       __se_sys_getdents+0xe4/0x250 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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:5868
       join_transaction+0x182/0xca0 fs/btrfs/transaction.c:320
       start_transaction+0x6b6/0x1620 fs/btrfs/transaction.c:705
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6270
       inode_update_time fs/inode.c:2117 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2190
       file_accessed include/linux/fs.h:2673 [inline]
       iterate_dir+0x44a/0x580 fs/readdir.c:111
       __do_sys_getdents fs/readdir.c:326 [inline]
       __se_sys_getdents+0xe4/0x250 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#5){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 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.h:1916 [inline]
       sb_start_intwrite include/linux/fs.h:2099 [inline]
       start_transaction+0x56e/0x1620 fs/btrfs/transaction.c:699
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6270
       inode_update_time fs/inode.c:2117 [inline]
       touch_atime+0x2f9/0x6d0 fs/inode.c:2190
       file_accessed include/linux/fs.h:2673 [inline]
       btrfs_file_mmap_prepare+0xde/0x150 fs/btrfs/file.c:2049
       vfs_mmap_prepare include/linux/fs.h:2410 [inline]
       call_mmap_prepare mm/vma.c:2586 [inline]
       __mmap_region mm/vma.c:2654 [inline]
       mmap_region+0xb52/0x20f0 mm/vma.c:2740
       do_mmap+0xc23/0x10c0 mm/mmap.c:558
       vm_mmap_pgoff+0x2a9/0x4d0 mm/util.c:581
       ksys_mmap_pgoff+0x4e9/0x720 mm/mmap.c:604
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 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#5 --> &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#5);

 *** DEADLOCK ***

2 locks held by syz.4.264/7405:
 #0: ffff88803b503050 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:330 [inline]
 #0: ffff88803b503050 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x214/0x4d0 mm/util.c:579
 #1: ffff8880632e4480 (sb_writers#22){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2673 [inline]
 #1: ffff8880632e4480 (sb_writers#22){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0xde/0x150 fs/btrfs/file.c:2049

stack backtrace:
CPU: 0 UID: 0 PID: 7405 Comm: syz.4.264 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 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.h:1916 [inline]
 sb_start_intwrite include/linux/fs.h:2099 [inline]
 start_transaction+0x56e/0x1620 fs/btrfs/transaction.c:699
 btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6270
 inode_update_time fs/inode.c:2117 [inline]
 touch_atime+0x2f9/0x6d0 fs/inode.c:2190
 file_accessed include/linux/fs.h:2673 [inline]
 btrfs_file_mmap_prepare+0xde/0x150 fs/btrfs/file.c:2049
 vfs_mmap_prepare include/linux/fs.h:2410 [inline]
 call_mmap_prepare mm/vma.c:2586 [inline]
 __mmap_region mm/vma.c:2654 [inline]
 mmap_region+0xb52/0x20f0 mm/vma.c:2740
 do_mmap+0xc23/0x10c0 mm/mmap.c:558
 vm_mmap_pgoff+0x2a9/0x4d0 mm/util.c:581
 ksys_mmap_pgoff+0x4e9/0x720 mm/mmap.c:604
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9dab9af6c9
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:00007f9da9c16038 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f9dabc05fa0 RCX: 00007f9dab9af6c9
RDX: 00000000027ffff7 RSI: 0000000000600000 RDI: 0000200000000000
RBP: 00007f9daba31f91 R08: 0000000000000004 R09: 0000000000000000
R10: 0000000004012011 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9dabc06038 R14: 00007f9dabc05fa0 R15: 00007ffcfeb9bda8
 </TASK>