syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.7.731/12125 is trying to acquire lock:
ffff888035640770 (sb_internal#2){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6324

but task is already holding lock:
ffff8880356405f8 (sb_pagefaults#6){.+.+}-{0:0}, at: do_page_mkwrite+0x150/0x310 mm/memory.c:3528

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (sb_pagefaults#6){.+.+}-{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+0x32c/0x1a80 fs/btrfs/file.c:1875
       do_page_mkwrite+0x150/0x310 mm/memory.c:3528
       wp_page_shared mm/memory.c:3929 [inline]
       do_wp_page+0x25e8/0x4970 mm/memory.c:4148
       handle_pte_fault mm/memory.c:6289 [inline]
       __handle_mm_fault mm/memory.c:6411 [inline]
       handle_mm_fault+0x9f6/0x1330 mm/memory.c:6580
       do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x71/0xd0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

-> #6 (vm_lock){++++}-{0:0}:
       __vma_enter_locked+0x23a/0x730 mm/mmap_lock.c:72
       __vma_start_write+0x23/0x140 mm/mmap_lock.c:104
       vma_start_write include/linux/mmap_lock.h:213 [inline]
       mprotect_fixup+0x5af/0xa30 mm/mprotect.c:768
       setup_arg_pages+0x52a/0xa90 fs/exec.c:670
       load_elf_binary+0xbad/0x2750 fs/binfmt_elf.c:1028
       search_binary_handler fs/exec.c:1669 [inline]
       exec_binprm fs/exec.c:1701 [inline]
       bprm_execve+0x92e/0x1400 fs/exec.c:1753
       kernel_execve+0x8f0/0x9f0 fs/exec.c:1919
       try_to_run_init_process+0x13/0x60 init/main.c:1506
       kernel_init+0xad/0x1d0 init/main.c:1634
       ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

-> #5 (&mm->mmap_lock){++++}-{4:4}:
       down_read_killable+0x9d/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+0x2a8/0x300 mm/mmap_lock.c:450
       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+0x71/0xd0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
       user_access_begin arch/x86/include/asm/uaccess.h:-1 [inline]
       filldir+0x29c/0x6c0 fs/readdir.c:290
       dir_emit include/linux/fs.h:3527 [inline]
       kernfs_fop_readdir+0x53a/0x870 fs/kernfs/dir.c:1915
       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+0xec/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+0x123/0x280 fs/sysfs/dir.c:59
       create_dir lib/kobject.c:73 [inline]
       kobject_add_internal+0x6b1/0xcd0 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:2697
       btrfs_quota_enable+0x25d/0x28f0 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+0xec/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+0x29c/0x28f0 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+0xec/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+0x6b7/0x15f0 fs/btrfs/transaction.c:707
       __unlink_start_trans fs/btrfs/inode.c:4418 [inline]
       btrfs_unlink+0x126/0x330 fs/btrfs/inode.c:4435
       vfs_unlink+0x386/0x650 fs/namei.c:5369
       do_unlinkat+0x2cf/0x570 fs/namei.c:5439
       __do_sys_unlink fs/namei.c:5474 [inline]
       __se_sys_unlink fs/namei.c:5472 [inline]
       __x64_sys_unlink+0x47/0x50 fs/namei.c:5472
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xec/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+0x6b7/0x15f0 fs/btrfs/transaction.c:707
       __unlink_start_trans fs/btrfs/inode.c:4418 [inline]
       btrfs_unlink+0x126/0x330 fs/btrfs/inode.c:4435
       vfs_unlink+0x386/0x650 fs/namei.c:5369
       do_unlinkat+0x2cf/0x570 fs/namei.c:5439
       __do_sys_unlink fs/namei.c:5474 [inline]
       __se_sys_unlink fs/namei.c:5472 [inline]
       __x64_sys_unlink+0x47/0x50 fs/namei.c:5472
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xec/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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x107/0x340 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+0x56f/0x15f0 fs/btrfs/transaction.c:701
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6324
       inode_update_time fs/inode.c:2167 [inline]
       file_update_time_flags+0x38d/0x4f0 fs/inode.c:2395
       btrfs_page_mkwrite+0x5dd/0x1a80 fs/btrfs/file.c:1916
       do_page_mkwrite+0x150/0x310 mm/memory.c:3528
       wp_page_shared mm/memory.c:3929 [inline]
       do_wp_page+0x25e8/0x4970 mm/memory.c:4148
       handle_pte_fault mm/memory.c:6289 [inline]
       __handle_mm_fault mm/memory.c:6411 [inline]
       handle_mm_fault+0x9f6/0x1330 mm/memory.c:6580
       do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336
       handle_page_fault arch/x86/mm/fault.c:1476 [inline]
       exc_page_fault+0x71/0xd0 arch/x86/mm/fault.c:1532
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

other info that might help us debug this:

Chain exists of:
  sb_internal#2 --> vm_lock --> sb_pagefaults#6

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(sb_pagefaults#6);
                               lock(vm_lock);
                               lock(sb_pagefaults#6);
  rlock(sb_internal#2);

 *** DEADLOCK ***

2 locks held by syz.7.731/12125:
 #0: ffff8880283f6bc8 (vm_lock){++++}-{0:0}, at: lock_vma_under_rcu+0x1a7/0x4a0 mm/mmap_lock.c:259
 #1: ffff8880356405f8 (sb_pagefaults#6){.+.+}-{0:0}, at: do_page_mkwrite+0x150/0x310 mm/memory.c:3528

stack backtrace:
CPU: 0 UID: 0 PID: 12125 Comm: syz.7.731 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x107/0x340 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+0x56f/0x15f0 fs/btrfs/transaction.c:701
 btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6324
 inode_update_time fs/inode.c:2167 [inline]
 file_update_time_flags+0x38d/0x4f0 fs/inode.c:2395
 btrfs_page_mkwrite+0x5dd/0x1a80 fs/btrfs/file.c:1916
 do_page_mkwrite+0x150/0x310 mm/memory.c:3528
 wp_page_shared mm/memory.c:3929 [inline]
 do_wp_page+0x25e8/0x4970 mm/memory.c:4148
 handle_pte_fault mm/memory.c:6289 [inline]
 __handle_mm_fault mm/memory.c:6411 [inline]
 handle_mm_fault+0x9f6/0x1330 mm/memory.c:6580
 do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x71/0xd0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7fb768a87398
Code: fc 89 37 c3 c5 fa 6f 06 c5 fa 6f 4c 16 f0 c5 fa 7f 07 c5 fa 7f 4c 17 f0 c3 66 0f 1f 84 00 00 00 00 00 48 8b 4c 16 f8 48 8b 36 <48> 89 37 48 89 4c 17 f8 c3 c5 fe 6f 54 16 e0 c5 fe 6f 5c 16 c0 c5
RSP: 002b:00007ffc6eb918e8 EFLAGS: 00010246
RAX: 0000200000000080 RBX: 0000000000000004 RCX: 0031656c69662f2e
RDX: 0000000000000008 RSI: 0031656c69662f2e RDI: 0000200000000080
RBP: 00007fb768d17da0 R08: 0000001b2d720000 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000009 R12: 00007fb768d15fac
R13: 00007fb768d15fa0 R14: fffffffffffffffe R15: 00007ffc6eb91a00
 </TASK>