syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.7478/29664 is trying to acquire lock:
ffff88805d838618 (sb_internal#2){.+.+}-{0:0}, at: btrfs_dirty_inode+0xc8/0x200 fs/btrfs/inode.c:6244

but task is already holding lock:
ffff88807d0a62a0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:415 [inline]
ffff88807d0a62a0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1f5/0x470 mm/util.c:578

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&mm->mmap_lock){++++}-{4:4}:
       down_write_killable+0x95/0x250 kernel/locking/rwsem.c:1601
       mmap_write_lock_killable include/linux/mmap_lock.h:415 [inline]
       upgrade_mmap_lock_carefully mm/mmap_lock.c:310 [inline]
       lock_mm_and_find_vma+0x1af/0x6e0 mm/mmap_lock.c:363
       do_user_addr_fault+0x2ac/0x1370 arch/x86/mm/fault.c:1359
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x5c/0xb0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
       filldir+0x1d3/0x600 fs/readdir.c:294
       dir_emit_dot include/linux/fs.h:3963 [inline]
       dir_emit_dots include/linux/fs.h:3974 [inline]
       offset_readdir+0x1c7/0x6d0 fs/libfs.c:569
       iterate_dir+0x296/0xaf0 fs/readdir.c:108
       __do_sys_getdents fs/readdir.c:326 [inline]
       __se_sys_getdents fs/readdir.c:312 [inline]
       __x64_sys_getdents+0x13c/0x2b0 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&type->i_mutex_dir_key#5){++++}-{4:4}:
       down_read+0x9b/0x480 kernel/locking/rwsem.c:1537
       inode_lock_shared include/linux/fs.h:885 [inline]
       lookup_slow fs/namei.c:1824 [inline]
       walk_component+0x345/0x5b0 fs/namei.c:2129
       lookup_last fs/namei.c:2630 [inline]
       path_lookupat+0x142/0x6d0 fs/namei.c:2654
       filename_lookup+0x224/0x5f0 fs/namei.c:2683
       kern_path+0x35/0x50 fs/namei.c:2816
       is_same_device fs/btrfs/volumes.c:759 [inline]
       device_list_add.constprop.0+0x7e3/0x2860 fs/btrfs/volumes.c:894
       btrfs_scan_one_device+0x30d/0x7f0 fs/btrfs/volumes.c:1493
       btrfs_get_tree_super fs/btrfs/super.c:1867 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2091 [inline]
       btrfs_get_tree+0x5a0/0x26f0 fs/btrfs/super.c:2125
       vfs_get_tree+0x8e/0x340 fs/super.c:1815
       do_new_mount fs/namespace.c:3808 [inline]
       path_mount+0x1513/0x2000 fs/namespace.c:4123
       do_mount fs/namespace.c:4136 [inline]
       __do_sys_mount fs/namespace.c:4347 [inline]
       __se_sys_mount fs/namespace.c:4324 [inline]
       __x64_sys_mount+0x28d/0x310 fs/namespace.c:4324
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&fs_devs->device_list_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
       insert_dev_extents fs/btrfs/block-group.c:2754 [inline]
       btrfs_create_pending_block_groups+0x771/0x1990 fs/btrfs/block-group.c:2805
       __btrfs_end_transaction+0xf5/0x920 fs/btrfs/transaction.c:1071
       flush_space+0x887/0xe40 fs/btrfs/space-info.c:865
       do_async_reclaim_metadata_space+0x18d/0x3e0 fs/btrfs/space-info.c:1158
       btrfs_async_reclaim_metadata_space+0xd0/0x160 fs/btrfs/space-info.c:1226
       process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3236
       process_scheduled_works kernel/workqueue.c:3319 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
       kthread+0x3c5/0x780 kernel/kthread.c:463
       ret_from_fork+0x56d/0x730 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x165/0x1020 fs/btrfs/transaction.c:321
       start_transaction+0x430/0x1b00 fs/btrfs/transaction.c:705
       btrfs_rebuild_free_space_tree+0xad/0x870 fs/btrfs/free-space-tree.c:1339
       btrfs_start_pre_rw_mount+0x290/0x1ce0 fs/btrfs/disk-io.c:3075
       open_ctree+0x6b82/0x7550 fs/btrfs/disk-io.c:3617
       btrfs_fill_super fs/btrfs/super.c:991 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1954 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2091 [inline]
       btrfs_get_tree+0x1368/0x26f0 fs/btrfs/super.c:2125
       vfs_get_tree+0x8e/0x340 fs/super.c:1815
       do_new_mount fs/namespace.c:3808 [inline]
       path_mount+0x1513/0x2000 fs/namespace.c:4123
       do_mount fs/namespace.c:4136 [inline]
       __do_sys_mount fs/namespace.c:4347 [inline]
       __se_sys_mount fs/namespace.c:4324 [inline]
       __x64_sys_mount+0x28d/0x310 fs/namespace.c:4324
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x149/0x1020 fs/btrfs/transaction.c:320
       start_transaction+0x430/0x1b00 fs/btrfs/transaction.c:705
       btrfs_rebuild_free_space_tree+0xad/0x870 fs/btrfs/free-space-tree.c:1339
       btrfs_start_pre_rw_mount+0x290/0x1ce0 fs/btrfs/disk-io.c:3075
       open_ctree+0x6b82/0x7550 fs/btrfs/disk-io.c:3617
       btrfs_fill_super fs/btrfs/super.c:991 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1954 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2091 [inline]
       btrfs_get_tree+0x1368/0x26f0 fs/btrfs/super.c:2125
       vfs_get_tree+0x8e/0x340 fs/super.c:1815
       do_new_mount fs/namespace.c:3808 [inline]
       path_mount+0x1513/0x2000 fs/namespace.c:4123
       do_mount fs/namespace.c:4136 [inline]
       __do_sys_mount fs/namespace.c:4347 [inline]
       __se_sys_mount fs/namespace.c:4324 [inline]
       __x64_sys_mount+0x28d/0x310 fs/namespace.c:4324
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_internal#2){.+.+}-{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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
       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:1799 [inline]
       sb_start_intwrite include/linux/fs.h:1982 [inline]
       start_transaction+0xbe3/0x1b00 fs/btrfs/transaction.c:699
       btrfs_dirty_inode+0xc8/0x200 fs/btrfs/inode.c:6244
       btrfs_update_time fs/btrfs/inode.c:6278 [inline]
       btrfs_update_time+0xb2/0xf0 fs/btrfs/inode.c:6269
       inode_update_time fs/inode.c:2075 [inline]
       touch_atime+0x352/0x5d0 fs/inode.c:2148
       file_accessed include/linux/fs.h:2664 [inline]
       btrfs_file_mmap_prepare+0x132/0x180 fs/btrfs/file.c:2050
       vfs_mmap_prepare include/linux/fs.h:2295 [inline]
       call_mmap_prepare mm/vma.c:2585 [inline]
       __mmap_region+0xee5/0x27b0 mm/vma.c:2653
       mmap_region+0x32b/0x3f0 mm/vma.c:2739
       do_mmap+0xa3e/0x1210 mm/mmap.c:558
       vm_mmap_pgoff+0x29e/0x470 mm/util.c:580
       ksys_mmap_pgoff+0x32c/0x5c0 mm/mmap.c:604
       __do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline]
       __se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline]
       __x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4e0 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#2 --> &type->i_mutex_dir_key#5 --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_lock);
                               lock(&type->i_mutex_dir_key#5);
                               lock(&mm->mmap_lock);
  rlock(sb_internal#2);

 *** DEADLOCK ***

2 locks held by syz.3.7478/29664:
 #0: ffff88807d0a62a0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:415 [inline]
 #0: ffff88807d0a62a0 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1f5/0x470 mm/util.c:578
 #1: ffff88805d838428 (sb_writers#18){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2664 [inline]
 #1: ffff88805d838428 (sb_writers#18){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0x132/0x180 fs/btrfs/file.c:2050

stack backtrace:
CPU: 0 UID: 0 PID: 29664 Comm: syz.3.7478 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2043
 check_noncircular+0x14c/0x170 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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 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:1799 [inline]
 sb_start_intwrite include/linux/fs.h:1982 [inline]
 start_transaction+0xbe3/0x1b00 fs/btrfs/transaction.c:699
 btrfs_dirty_inode+0xc8/0x200 fs/btrfs/inode.c:6244
 btrfs_update_time fs/btrfs/inode.c:6278 [inline]
 btrfs_update_time+0xb2/0xf0 fs/btrfs/inode.c:6269
 inode_update_time fs/inode.c:2075 [inline]
 touch_atime+0x352/0x5d0 fs/inode.c:2148
 file_accessed include/linux/fs.h:2664 [inline]
 btrfs_file_mmap_prepare+0x132/0x180 fs/btrfs/file.c:2050
 vfs_mmap_prepare include/linux/fs.h:2295 [inline]
 call_mmap_prepare mm/vma.c:2585 [inline]
 __mmap_region+0xee5/0x27b0 mm/vma.c:2653
 mmap_region+0x32b/0x3f0 mm/vma.c:2739
 do_mmap+0xa3e/0x1210 mm/mmap.c:558
 vm_mmap_pgoff+0x29e/0x470 mm/util.c:580
 ksys_mmap_pgoff+0x32c/0x5c0 mm/mmap.c:604
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline]
 __x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2e14d8eec9
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:00007f2e15cc2038 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f2e14fe6090 RCX: 00007f2e14d8eec9
RDX: 0000000000000000 RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007f2e14e11f91 R08: 0000000000000004 R09: 0000000000000000
R10: 0000000000000013 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2e14fe6128 R14: 00007f2e14fe6090 R15: 00007ffc0087efe8
 </TASK>