syzbot

BTRFS info (device loop3): allowing degraded mounts
BTRFS info (device loop3): disabling tree log
BTRFS info (device loop3): turning on async discard
BTRFS info (device loop3): enabling free space tree
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.1033/14583 is trying to acquire lock:
ffff88801d6a2770 (sb_internal#2){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6364

but task is already holding lock:
ffff88801d6a25f8 (sb_pagefaults#5){.+.+}-{0:0}, at: do_page_mkwrite+0x150/0x310 mm/memory.c:3531

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (sb_pagefaults#5){.+.+}-{0:0}:
       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_pagefault include/linux/fs/super.h:159 [inline]
       btrfs_page_mkwrite+0x329/0x1b10 fs/btrfs/file.c:1875
       do_page_mkwrite+0x150/0x310 mm/memory.c:3531
       do_shared_fault mm/memory.c:5834 [inline]
       do_fault mm/memory.c:5896 [inline]
       do_pte_missing+0x763/0x2e60 mm/memory.c:4404
       handle_pte_fault mm/memory.c:6276 [inline]
       __handle_mm_fault mm/memory.c:6414 [inline]
       handle_mm_fault+0xd0a/0x13c0 mm/memory.c:6583
       do_user_addr_fault+0x75b/0x1360 arch/x86/mm/fault.c:1385
       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
       user_access_begin arch/x86/include/asm/uaccess.h:-1 [inline]
       filldir64+0x29c/0x670 fs/readdir.c:374
       dir_emit_dot include/linux/fs.h:3535 [inline]
       dir_emit_dots include/linux/fs.h:3546 [inline]
       btrfs_real_readdir+0x345/0x1550 fs/btrfs/inode.c:6245
       iterate_dir+0x3a5/0x580 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:412 [inline]
       __se_sys_getdents64+0xf1/0x280 fs/readdir.c:397
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0xa4/0x220 kernel/locking/rwsem.c:1560
       mmap_read_lock_killable+0x1d/0x70 include/linux/mmap_lock.h:400
       get_mmap_lock_carefully mm/mmap_lock.c:399 [inline]
       lock_mm_and_find_vma+0x2d7/0x340 mm/mmap_lock.c:450
       do_user_addr_fault+0x330/0x1360 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+0x2b5/0x690 fs/readdir.c:295
       dir_emit include/linux/fs.h:3531 [inline]
       kernfs_fop_readdir+0x57e/0x8d0 fs/kernfs/dir.c:1915
       iterate_dir+0x3a5/0x580 fs/readdir.c:108
       __do_sys_getdents fs/readdir.c:327 [inline]
       __se_sys_getdents+0xf1/0x270 fs/readdir.c:312
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 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:1590
       kernfs_add_one+0x41/0x5c0 fs/kernfs/dir.c:796
       kernfs_create_dir_ns+0xde/0x130 fs/kernfs/dir.c:1098
       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:2645
       btrfs_quota_enable+0x281/0x2940 fs/btrfs/qgroup.c:1002
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3613
       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+0xe2/0xf80 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:533 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552
       btrfs_quota_enable+0x2c3/0x2940 fs/btrfs/qgroup.c:1031
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3613
       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+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x1a4/0xc90 fs/btrfs/transaction.c:323
       start_transaction+0x6b9/0x15f0 fs/btrfs/transaction.c:708
       btrfs_rebuild_free_space_tree+0xbb/0x6e0 fs/btrfs/free-space-tree.c:1330
       btrfs_start_pre_rw_mount+0x12ed/0x1c50 fs/btrfs/disk-io.c:3031
       open_ctree+0x2ca7/0x3f00 fs/btrfs/disk-io.c:3599
       btrfs_fill_super fs/btrfs/super.c:981 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1944 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
       btrfs_get_tree+0x1061/0x1920 fs/btrfs/super.c:2121
       vfs_get_tree+0x92/0x2a0 fs/super.c:1751
       fc_mount fs/namespace.c:1199 [inline]
       do_new_mount_fc fs/namespace.c:3636 [inline]
       do_new_mount+0x329/0xa50 fs/namespace.c:3712
       do_mount fs/namespace.c:4035 [inline]
       __do_sys_mount fs/namespace.c:4224 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4201
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x182/0xc90 fs/btrfs/transaction.c:322
       start_transaction+0x6b9/0x15f0 fs/btrfs/transaction.c:708
       btrfs_rebuild_free_space_tree+0xbb/0x6e0 fs/btrfs/free-space-tree.c:1330
       btrfs_start_pre_rw_mount+0x12ed/0x1c50 fs/btrfs/disk-io.c:3031
       open_ctree+0x2ca7/0x3f00 fs/btrfs/disk-io.c:3599
       btrfs_fill_super fs/btrfs/super.c:981 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1944 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
       btrfs_get_tree+0x1061/0x1920 fs/btrfs/super.c:2121
       vfs_get_tree+0x92/0x2a0 fs/super.c:1751
       fc_mount fs/namespace.c:1199 [inline]
       do_new_mount_fc fs/namespace.c:3636 [inline]
       do_new_mount+0x329/0xa50 fs/namespace.c:3712
       do_mount fs/namespace.c:4035 [inline]
       __do_sys_mount fs/namespace.c:4224 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4201
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x330 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+0x56e/0x15f0 fs/btrfs/transaction.c:702
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6364
       inode_update_time fs/inode.c:2170 [inline]
       file_update_time_flags+0x38d/0x4e0 fs/inode.c:2398
       btrfs_page_mkwrite+0x5df/0x1b10 fs/btrfs/file.c:1916
       do_page_mkwrite+0x150/0x310 mm/memory.c:3531
       do_shared_fault mm/memory.c:5834 [inline]
       do_fault mm/memory.c:5896 [inline]
       do_pte_missing+0x763/0x2e60 mm/memory.c:4404
       handle_pte_fault mm/memory.c:6276 [inline]
       __handle_mm_fault mm/memory.c:6414 [inline]
       handle_mm_fault+0xd0a/0x13c0 mm/memory.c:6583
       do_user_addr_fault+0x75b/0x1360 arch/x86/mm/fault.c:1385
       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
       user_access_begin arch/x86/include/asm/uaccess.h:-1 [inline]
       filldir64+0x29c/0x670 fs/readdir.c:374
       dir_emit_dot include/linux/fs.h:3535 [inline]
       dir_emit_dots include/linux/fs.h:3546 [inline]
       btrfs_real_readdir+0x345/0x1550 fs/btrfs/inode.c:6245
       iterate_dir+0x3a5/0x580 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:412 [inline]
       __se_sys_getdents64+0xf1/0x280 fs/readdir.c:397
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 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#2 --> &mm->mmap_lock --> sb_pagefaults#5

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

4 locks held by syz.3.1033/14583:
 #0: ffff888037754328 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1255
 #1: ffff88805e38afb0 (&type->i_mutex_dir_key#8){++++}-{4:4}, at: iterate_dir+0x29e/0x580 fs/readdir.c:101
 #2: ffff8880589e83b0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:410 [inline]
 #2: ffff8880589e83b0 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:390 [inline]
 #2: ffff8880589e83b0 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340 mm/mmap_lock.c:450
 #3: ffff88801d6a25f8 (sb_pagefaults#5){.+.+}-{0:0}, at: do_page_mkwrite+0x150/0x310 mm/memory.c:3531

stack backtrace:
CPU: 0 UID: 0 PID: 14583 Comm: syz.3.1033 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
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+0x106/0x330 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+0x56e/0x15f0 fs/btrfs/transaction.c:702
 btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6364
 inode_update_time fs/inode.c:2170 [inline]
 file_update_time_flags+0x38d/0x4e0 fs/inode.c:2398
 btrfs_page_mkwrite+0x5df/0x1b10 fs/btrfs/file.c:1916
 do_page_mkwrite+0x150/0x310 mm/memory.c:3531
 do_shared_fault mm/memory.c:5834 [inline]
 do_fault mm/memory.c:5896 [inline]
 do_pte_missing+0x763/0x2e60 mm/memory.c:4404
 handle_pte_fault mm/memory.c:6276 [inline]
 __handle_mm_fault mm/memory.c:6414 [inline]
 handle_mm_fault+0xd0a/0x13c0 mm/memory.c:6583
 do_user_addr_fault+0x75b/0x1360 arch/x86/mm/fault.c:1385
 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
RIP: 0010:filldir64+0x29c/0x670 fs/readdir.c:378
Code: 88 ff 4c 89 ff 4c 89 e6 e8 71 b0 88 ff 4d 39 e7 0f 82 5b 02 00 00 49 39 ef 0f 87 52 02 00 00 0f 01 cb 0f ae e8 48 8b 44 24 50 <49> 89 44 24 08 48 8b 4c 24 08 48 8b 44 24 58 48 89 01 48 8b 04 24
RSP: 0018:ffffc900044f7aa8 EFLAGS: 00050283
RAX: 0000000000000000 RBX: ffffc900044f7e38 RCX: ffff88802bac9e40
RDX: 0000000000000002 RSI: 0000200000001f80 RDI: 0000200000001f98
RBP: 00007ffffffff000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000100 R11: ffffffff823a8420 R12: 0000200000001f80
R13: ffffffff8b74d6a0 R14: 0000000000000001 R15: 0000200000001f98
 dir_emit_dot include/linux/fs.h:3535 [inline]
 dir_emit_dots include/linux/fs.h:3546 [inline]
 btrfs_real_readdir+0x345/0x1550 fs/btrfs/inode.c:6245
 iterate_dir+0x3a5/0x580 fs/readdir.c:108
 __do_sys_getdents64 fs/readdir.c:412 [inline]
 __se_sys_getdents64+0xf1/0x280 fs/readdir.c:397
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe951eaaeb9
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:00007fe950106028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007fe952125fa0 RCX: 00007fe951eaaeb9
RDX: 0000000000001001 RSI: 0000200000001f80 RDI: 0000000000000006
RBP: 00007fe951f18c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe952126038 R14: 00007fe952125fa0 R15: 00007ffdc41ea808
 </TASK>
cgroup: name respecified
----------------
Code disassembly (best guess):
   0:	88 ff                	mov    %bh,%bh
   2:	4c 89 ff             	mov    %r15,%rdi
   5:	4c 89 e6             	mov    %r12,%rsi
   8:	e8 71 b0 88 ff       	call   0xff88b07e
   d:	4d 39 e7             	cmp    %r12,%r15
  10:	0f 82 5b 02 00 00    	jb     0x271
  16:	49 39 ef             	cmp    %rbp,%r15
  19:	0f 87 52 02 00 00    	ja     0x271
  1f:	0f 01 cb             	stac
  22:	0f ae e8             	lfence
  25:	48 8b 44 24 50       	mov    0x50(%rsp),%rax
* 2a:	49 89 44 24 08       	mov    %rax,0x8(%r12) <-- trapping instruction
  2f:	48 8b 4c 24 08       	mov    0x8(%rsp),%rcx
  34:	48 8b 44 24 58       	mov    0x58(%rsp),%rax
  39:	48 89 01             	mov    %rax,(%rcx)
  3c:	48 8b 04 24          	mov    (%rsp),%rax