syzbot

BTRFS info (device loop0): use zstd compression, level 3
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.0.263/8377 is trying to acquire lock:
ffff0000d2490610 (sb_internal#2){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:832

but task is already holding lock:
ffff0000c671d700 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:353 [inline]
ffff0000c671d700 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dc/0x45c 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+0x60/0x344 kernel/locking/rwsem.c:1560
       mmap_read_lock_killable+0x28/0x8c include/linux/mmap_lock.h:400
       get_mmap_lock_carefully mm/mmap_lock.c:399 [inline]
       lock_mm_and_find_vma+0x2a4/0x2d8 mm/mmap_lock.c:450
       do_page_fault+0x50c/0x13cc arch/arm64/mm/fault.c:678
       do_translation_fault+0xc4/0x114 arch/arm64/mm/fault.c:793
       do_mem_abort+0x70/0x194 arch/arm64/mm/fault.c:933
       el1_abort+0x40/0x64 arch/arm64/kernel/entry-common.c:303
       el1h_64_sync_handler+0x50/0xfc arch/arm64/kernel/entry-common.c:437
       el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:591
       __uaccess_mask_ptr arch/arm64/include/asm/uaccess.h:169 [inline]
       filldir64+0x314/0x6bc fs/readdir.c:381
       dir_emit include/linux/fs.h:3527 [inline]
       kernfs_fop_readdir+0x498/0x79c fs/kernfs/dir.c:1913
       iterate_dir+0x2dc/0x478 fs/readdir.c:108
       __do_sys_getdents64 fs/readdir.c:410 [inline]
       __se_sys_getdents64 fs/readdir.c:396 [inline]
       __arm64_sys_getdents64+0x110/0x2fc fs/readdir.c:396
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #4 (&root->kernfs_rwsem){++++}-{4:4}:
       down_write+0x50/0xc0 kernel/locking/rwsem.c:1590
       kernfs_add_one+0x48/0x574 fs/kernfs/dir.c:794
       kernfs_create_dir_ns+0xd4/0x12c fs/kernfs/dir.c:1096
       sysfs_create_dir_ns+0x114/0x24c fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x5a8/0xb48 lib/kobject.c:240
       kobject_add_varg lib/kobject.c:374 [inline]
       kobject_init_and_add+0x118/0x17c lib/kobject.c:457
       btrfs_sysfs_add_qgroups+0x110/0x268 fs/btrfs/sysfs.c:2697
       btrfs_quota_enable+0x20c/0x247c fs/btrfs/qgroup.c:1002
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3613
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5296
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #3 (&fs_info->qgroup_ioctl_lock){+.+.}-{4:4}:
       __mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:614
       __mutex_lock kernel/locking/mutex.c:776 [inline]
       mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:828
       btrfs_quota_enable+0x24c/0x247c fs/btrfs/qgroup.c:1031
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3613
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5296
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x190/0xb5c fs/btrfs/transaction.c:323
       start_transaction+0x778/0x1530 fs/btrfs/transaction.c:707
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:818
       btrfs_rebuild_free_space_tree+0xac/0x6c0 fs/btrfs/free-space-tree.c:1330
       btrfs_start_pre_rw_mount+0xed8/0x1728 fs/btrfs/disk-io.c:3052
       open_ctree+0x24cc/0x358c fs/btrfs/disk-io.c:3603
       btrfs_fill_super fs/btrfs/super.c:983 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1946 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2089 [inline]
       btrfs_get_tree+0xd94/0x15dc fs/btrfs/super.c:2123
       vfs_get_tree+0x90/0x28c fs/super.c:1751
       fc_mount fs/namespace.c:1199 [inline]
       do_new_mount_fc fs/namespace.c:3636 [inline]
       do_new_mount+0x284/0x944 fs/namespace.c:3712
       path_mount+0x5b4/0xdfc fs/namespace.c:4022
       do_mount fs/namespace.c:4035 [inline]
       __do_sys_mount fs/namespace.c:4224 [inline]
       __se_sys_mount fs/namespace.c:4201 [inline]
       __arm64_sys_mount+0x3e8/0x468 fs/namespace.c:4201
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0x164/0xb5c fs/btrfs/transaction.c:322
       start_transaction+0x778/0x1530 fs/btrfs/transaction.c:707
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:818
       btrfs_rebuild_free_space_tree+0xac/0x6c0 fs/btrfs/free-space-tree.c:1330
       btrfs_start_pre_rw_mount+0xed8/0x1728 fs/btrfs/disk-io.c:3052
       open_ctree+0x24cc/0x358c fs/btrfs/disk-io.c:3603
       btrfs_fill_super fs/btrfs/super.c:983 [inline]
       btrfs_get_tree_super fs/btrfs/super.c:1946 [inline]
       btrfs_get_tree_subvol fs/btrfs/super.c:2089 [inline]
       btrfs_get_tree+0xd94/0x15dc fs/btrfs/super.c:2123
       vfs_get_tree+0x90/0x28c fs/super.c:1751
       fc_mount fs/namespace.c:1199 [inline]
       do_new_mount_fc fs/namespace.c:3636 [inline]
       do_new_mount+0x284/0x944 fs/namespace.c:3712
       path_mount+0x5b4/0xdfc fs/namespace.c:4022
       do_mount fs/namespace.c:4035 [inline]
       __do_sys_mount fs/namespace.c:4224 [inline]
       __se_sys_mount fs/namespace.c:4201 [inline]
       __arm64_sys_mount+0x3e8/0x468 fs/namespace.c:4201
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #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+0x1774/0x30a4 kernel/locking/lockdep.c:5237
       lock_acquire+0x140/0x2e0 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+0x5bc/0x1530 fs/btrfs/transaction.c:701
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:832
       btrfs_dirty_inode+0x90/0x190 fs/btrfs/inode.c:6323
       btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6357
       inode_update_time fs/inode.c:2167 [inline]
       touch_atime+0x2e4/0x818 fs/inode.c:2240
       file_accessed include/linux/fs.h:2254 [inline]
       btrfs_file_mmap_prepare+0x148/0x1c4 fs/btrfs/file.c:2052
       vfs_mmap_prepare include/linux/fs.h:2058 [inline]
       call_mmap_prepare mm/vma.c:2596 [inline]
       __mmap_region mm/vma.c:2692 [inline]
       mmap_region+0x910/0x1978 mm/vma.c:2786
       do_mmap+0x968/0xfac mm/mmap.c:558
       vm_mmap_pgoff+0x2d8/0x45c mm/util.c:581
       ksys_mmap_pgoff+0x394/0x5b8 mm/mmap.c:604
       __do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
       __se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
       __arm64_sys_mmap+0xf8/0x110 arch/arm64/kernel/sys.c:21
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

other info that might help us debug this:

Chain exists of:
  sb_internal#2 --> &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#2);

 *** DEADLOCK ***

2 locks held by syz.0.263/8377:
 #0: ffff0000c671d700 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:353 [inline]
 #0: ffff0000c671d700 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dc/0x45c mm/util.c:579
 #1: ffff0000d2490420 (sb_writers#15){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2254 [inline]
 #1: ffff0000d2490420 (sb_writers#15){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0x148/0x1c4 fs/btrfs/file.c:2052

stack backtrace:
CPU: 0 UID: 0 PID: 8377 Comm: syz.0.263 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 dump_stack+0x1c/0x28 lib/dump_stack.c:129
 print_circular_bug+0x324/0x32c kernel/locking/lockdep.c:2043
 check_noncircular+0x154/0x174 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+0x1774/0x30a4 kernel/locking/lockdep.c:5237
 lock_acquire+0x140/0x2e0 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+0x5bc/0x1530 fs/btrfs/transaction.c:701
 btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:832
 btrfs_dirty_inode+0x90/0x190 fs/btrfs/inode.c:6323
 btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6357
 inode_update_time fs/inode.c:2167 [inline]
 touch_atime+0x2e4/0x818 fs/inode.c:2240
 file_accessed include/linux/fs.h:2254 [inline]
 btrfs_file_mmap_prepare+0x148/0x1c4 fs/btrfs/file.c:2052
 vfs_mmap_prepare include/linux/fs.h:2058 [inline]
 call_mmap_prepare mm/vma.c:2596 [inline]
 __mmap_region mm/vma.c:2692 [inline]
 mmap_region+0x910/0x1978 mm/vma.c:2786
 do_mmap+0x968/0xfac mm/mmap.c:558
 vm_mmap_pgoff+0x2d8/0x45c mm/util.c:581
 ksys_mmap_pgoff+0x394/0x5b8 mm/mmap.c:604
 __do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
 __se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
 __arm64_sys_mmap+0xf8/0x110 arch/arm64/kernel/sys.c:21
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x5c/0x26c arch/arm64/kernel/entry-common.c:724
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596