syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.87/6485 is trying to acquire lock:
ffff88804036c770 (sb_internal#5){.+.+}-{0:0}, at: btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6414

but task is already holding lock:
ffff88804036c5f8 (sb_pagefaults#2){.+.+}-{0:0}, at: do_page_mkwrite+0x150/0x310 mm/memory.c:3589

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #6 (sb_pagefaults#2){.+.+}-{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:1873
       do_page_mkwrite+0x150/0x310 mm/memory.c:3589
       do_shared_fault mm/memory.c:5874 [inline]
       do_fault mm/memory.c:5936 [inline]
       do_pte_missing+0x729/0x2d30 mm/memory.c:4477
       handle_pte_fault mm/memory.c:6316 [inline]
       __handle_mm_fault mm/memory.c:6454 [inline]
       handle_mm_fault+0xd0a/0x13c0 mm/memory.c:6623
       do_user_addr_fault+0x75b/0x1340 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

-> #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:601
       get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
       lock_mm_and_find_vma+0x2d7/0x340 mm/mmap_lock.c:501
       do_user_addr_fault+0x330/0x1340 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
       filldir64+0x2c0/0x670 fs/readdir.c:-1
       dir_emit include/linux/fs.h:3566 [inline]
       kernfs_fop_readdir+0x57e/0x8d0 fs/kernfs/dir.c:1915
       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+0x14d/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:2604
       btrfs_quota_enable+0x282/0x2850 fs/btrfs/qgroup.c:1034
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3533
       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+0x14d/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+0x2c6/0x2850 fs/btrfs/qgroup.c:1063
       btrfs_ioctl_quota_ctl+0x186/0x1c0 fs/btrfs/ioctl.c:3533
       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+0x14d/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+0x6b9/0x1650 fs/btrfs/transaction.c:708
       btrfs_rebuild_free_space_tree+0xbb/0x6e0 fs/btrfs/free-space-tree.c:1328
       btrfs_start_pre_rw_mount+0x1529/0x1f20 fs/btrfs/disk-io.c:3061
       open_ctree+0x2e04/0x4220 fs/btrfs/disk-io.c:3653
       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+0x1061/0x1930 fs/btrfs/super.c:2121
       vfs_get_tree+0x92/0x2a0 fs/super.c:1754
       fc_mount fs/namespace.c:1193 [inline]
       do_new_mount_fc fs/namespace.c:3763 [inline]
       do_new_mount+0x341/0xd30 fs/namespace.c:3839
       do_mount fs/namespace.c:4172 [inline]
       __do_sys_mount fs/namespace.c:4361 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4338
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/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+0x6b9/0x1650 fs/btrfs/transaction.c:708
       btrfs_rebuild_free_space_tree+0xbb/0x6e0 fs/btrfs/free-space-tree.c:1328
       btrfs_start_pre_rw_mount+0x1529/0x1f20 fs/btrfs/disk-io.c:3061
       open_ctree+0x2e04/0x4220 fs/btrfs/disk-io.c:3653
       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+0x1061/0x1930 fs/btrfs/super.c:2121
       vfs_get_tree+0x92/0x2a0 fs/super.c:1754
       fc_mount fs/namespace.c:1193 [inline]
       do_new_mount_fc fs/namespace.c:3763 [inline]
       do_new_mount+0x341/0xd30 fs/namespace.c:3839
       do_mount fs/namespace.c:4172 [inline]
       __do_sys_mount fs/namespace.c:4361 [inline]
       __se_sys_mount+0x31d/0x420 fs/namespace.c:4338
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0xf0/0x2e0 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+0x56e/0x1650 fs/btrfs/transaction.c:702
       btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6414
       file_update_time_flags+0x2d5/0x4b0 fs/inode.c:2426
       btrfs_page_mkwrite+0x5df/0x1b10 fs/btrfs/file.c:1914
       do_page_mkwrite+0x150/0x310 mm/memory.c:3589
       do_shared_fault mm/memory.c:5874 [inline]
       do_fault mm/memory.c:5936 [inline]
       do_pte_missing+0x729/0x2d30 mm/memory.c:4477
       handle_pte_fault mm/memory.c:6316 [inline]
       __handle_mm_fault mm/memory.c:6454 [inline]
       handle_mm_fault+0xd0a/0x13c0 mm/memory.c:6623
       do_user_addr_fault+0x75b/0x1340 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

other info that might help us debug this:

Chain exists of:
  sb_internal#5 --> &mm->mmap_lock --> sb_pagefaults#2

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz.2.87/6485:
 #0: ffff88802d955cf0 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_trylock include/linux/mmap_lock.h:611 [inline]
 #0: ffff88802d955cf0 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:441 [inline]
 #0: ffff88802d955cf0 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x36/0x340 mm/mmap_lock.c:501
 #1: ffff88804036c5f8 (sb_pagefaults#2){.+.+}-{0:0}, at: do_page_mkwrite+0x150/0x310 mm/memory.c:3589

stack backtrace:
CPU: 1 UID: 0 PID: 6485 Comm: syz.2.87 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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+0xf0/0x2e0 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+0x56e/0x1650 fs/btrfs/transaction.c:702
 btrfs_dirty_inode+0x9f/0x190 fs/btrfs/inode.c:6414
 file_update_time_flags+0x2d5/0x4b0 fs/inode.c:2426
 btrfs_page_mkwrite+0x5df/0x1b10 fs/btrfs/file.c:1914
 do_page_mkwrite+0x150/0x310 mm/memory.c:3589
 do_shared_fault mm/memory.c:5874 [inline]
 do_fault mm/memory.c:5936 [inline]
 do_pte_missing+0x729/0x2d30 mm/memory.c:4477
 handle_pte_fault mm/memory.c:6316 [inline]
 __handle_mm_fault mm/memory.c:6454 [inline]
 handle_mm_fault+0xd0a/0x13c0 mm/memory.c:6623
 do_user_addr_fault+0x75b/0x1340 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: 0033:0x7ff935eab5dd
Code: 00 66 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 83 fa 20 72 37 c5 fe 6f 06 48 83 fa 40 0f 87 b9 00 00 00 c5 fe 6f 4c 16 e0 <c5> fe 7f 07 c5 fe 7f 4c 17 e0 0f 01 d6 75 04 c5 f8 77 c3 c5 fc 77
RSP: 002b:00007ffd89452cb8 EFLAGS: 00010287
RAX: 0000200000000440 RBX: 0000000000000004 RCX: 0000000000000000
RDX: 0000000000000039 RSI: 0000001b2de2af3d RDI: 0000200000000440
RBP: fffffffffffffffe R08: 0000001b2e220000 R09: 0000000000000072
R10: 0000000000000039 R11: 0000000000000000 R12: 00007ffd89452de0
R13: 00007ff936155fac R14: 0000000000025b14 R15: 00007ffd89452dc0
 </TASK>