syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.326/8641 is trying to acquire lock:
ffff0000c7320610 (sb_internal#5){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830

but task is already holding lock:
ffff0000d8a51d90 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:330 [inline]
ffff0000d8a51d90 (&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+0x60/0x32c kernel/locking/rwsem.c:1560
       mmap_read_lock_killable+0x28/0x8c include/linux/mmap_lock.h:377
       get_mmap_lock_carefully mm/mmap_lock.c:377 [inline]
       lock_mm_and_find_vma+0x2a4/0x2d8 mm/mmap_lock.c:428
       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+0x2ec/0x6bc fs/readdir.c:379
       dir_emit include/linux/fs.h:3988 [inline]
       kernfs_fop_readdir+0x498/0x79c fs/kernfs/dir.c:1910
       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/0x254 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+0x48/0x60c fs/kernfs/dir.c:791
       kernfs_create_dir_ns+0xd4/0x12c fs/kernfs/dir.c:1093
       sysfs_create_dir_ns+0x114/0x24c fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x5a8/0xb20 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:2645
       btrfs_quota_enable+0x210/0x2438 fs/btrfs/qgroup.c:1022
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3667
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5333
       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/0x254 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:598
       __mutex_lock kernel/locking/mutex.c:760 [inline]
       mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
       btrfs_quota_enable+0x24c/0x2438 fs/btrfs/qgroup.c:1051
       btrfs_ioctl_quota_ctl+0x178/0x1bc fs/btrfs/ioctl.c:3667
       btrfs_ioctl+0x86c/0xc3c fs/btrfs/ioctl.c:5333
       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/0x254 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:321
       start_transaction+0x778/0x155c fs/btrfs/transaction.c:705
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:816
       btrfs_create_common+0x120/0x208 fs/btrfs/inode.c:6786
       btrfs_mkdir+0xc4/0xec fs/btrfs/inode.c:6928
       vfs_mkdir+0x284/0x424 fs/namei.c:4453
       do_mkdirat+0x1f8/0x4c8 fs/namei.c:4486
       __do_sys_mkdirat fs/namei.c:4503 [inline]
       __se_sys_mkdirat fs/namei.c:4501 [inline]
       __arm64_sys_mkdirat+0x8c/0xa4 fs/namei.c:4501
       __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/0x254 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:320
       start_transaction+0x778/0x155c fs/btrfs/transaction.c:705
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:816
       btrfs_create_common+0x120/0x208 fs/btrfs/inode.c:6786
       btrfs_mkdir+0xc4/0xec fs/btrfs/inode.c:6928
       vfs_mkdir+0x284/0x424 fs/namei.c:4453
       do_mkdirat+0x1f8/0x4c8 fs/namei.c:4486
       __do_sys_mkdirat fs/namei.c:4503 [inline]
       __se_sys_mkdirat fs/namei.c:4501 [inline]
       __arm64_sys_mkdirat+0x8c/0xa4 fs/namei.c:4501
       __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/0x254 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#5){.+.+}-{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+0x14c/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.h:1916 [inline]
       sb_start_intwrite include/linux/fs.h:2099 [inline]
       start_transaction+0x5bc/0x155c fs/btrfs/transaction.c:699
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830
       btrfs_dirty_inode+0x90/0x190 fs/btrfs/inode.c:6272
       btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6306
       inode_update_time fs/inode.c:2129 [inline]
       touch_atime+0x2e4/0x818 fs/inode.c:2202
       file_accessed include/linux/fs.h:2673 [inline]
       btrfs_file_mmap_prepare+0xc4/0x130 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+0x940/0x1d28 mm/vma.c:2740
       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/0x254 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#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.0.326/8641:
 #0: ffff0000d8a51d90 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:330 [inline]
 #0: ffff0000d8a51d90 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1dc/0x45c mm/util.c:579
 #1: ffff0000c7320420 (sb_writers#16){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2673 [inline]
 #1: ffff0000c7320420 (sb_writers#16){.+.+}-{0:0}, at: btrfs_file_mmap_prepare+0xc4/0x130 fs/btrfs/file.c:2049

stack backtrace:
CPU: 1 UID: 0 PID: 8641 Comm: syz.0.326 Not tainted syzkaller #0 PREEMPT 
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+0x14c/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.h:1916 [inline]
 sb_start_intwrite include/linux/fs.h:2099 [inline]
 start_transaction+0x5bc/0x155c fs/btrfs/transaction.c:699
 btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:830
 btrfs_dirty_inode+0x90/0x190 fs/btrfs/inode.c:6272
 btrfs_update_time+0xa0/0xd0 fs/btrfs/inode.c:6306
 inode_update_time fs/inode.c:2129 [inline]
 touch_atime+0x2e4/0x818 fs/inode.c:2202
 file_accessed include/linux/fs.h:2673 [inline]
 btrfs_file_mmap_prepare+0xc4/0x130 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+0x940/0x1d28 mm/vma.c:2740
 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/0x254 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