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Message-ID: <000000000000a8a5cc05ec7f35fd@google.com>
Date:   Wed, 02 Nov 2022 09:19:48 -0700
From:   syzbot <syzbot+a033efd03287efd49df1@...kaller.appspotmail.com>
To:     clm@...com, dsterba@...e.com, josef@...icpanda.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: [syzbot] possible deadlock in btrfs_lock_root_node

Hello,

syzbot found the following issue on:

HEAD commit:    bbed346d5a96 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=10bc7961880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3a4a45d2d827c1e
dashboard link: https://syzkaller.appspot.com/bug?extid=a033efd03287efd49df1
compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e8e91bc79312/disk-bbed346d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c1cb3fb3b77e/vmlinux-bbed346d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a033efd03287efd49df1@...kaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.0.0-rc7-syzkaller-18095-gbbed346d5a96 #0 Not tainted
------------------------------------------------------
syz-executor.3/1107 is trying to acquire lock:
ffff000112e0b598 (&mm->mmap_lock){++++}-{3:3}, at: __might_fault+0x54/0xb4 mm/memory.c:5576

but task is already holding lock:
ffff00011a821388 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
ffff00011a821388 (btrfs-root-00){++++}-{3:3}, at: btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
ffff00011a821388 (btrfs-root-00){++++}-{3:3}, at: btrfs_read_lock_root_node+0x13c/0x1c0 fs/btrfs/locking.c:279

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (btrfs-root-00){++++}-{3:3}:
       down_write_nested+0x64/0xd8 kernel/locking/rwsem.c:1662
       __btrfs_tree_lock fs/btrfs/locking.c:196 [inline]
       btrfs_tree_lock fs/btrfs/locking.c:203 [inline]
       btrfs_lock_root_node+0x140/0x1d0 fs/btrfs/locking.c:256
       commit_cowonly_roots+0x64/0x3b8 fs/btrfs/transaction.c:1284
       btrfs_commit_transaction+0x948/0x12d8 fs/btrfs/transaction.c:2366
       btrfs_commit_super+0x84/0xa0 fs/btrfs/disk-io.c:4426
       close_ctree+0x1dc/0x60c fs/btrfs/disk-io.c:4580
       btrfs_put_super+0x20/0x30 fs/btrfs/super.c:392
       generic_shutdown_super+0x8c/0x190 fs/super.c:491
       kill_anon_super+0x24/0x44 fs/super.c:1085
       btrfs_kill_super+0x24/0x3c fs/btrfs/super.c:2440
       deactivate_locked_super+0x70/0xe8 fs/super.c:332
       deactivate_super+0xd0/0xd4 fs/super.c:363
       cleanup_mnt+0x1f8/0x234 fs/namespace.c:1186
       __cleanup_mnt+0x20/0x30 fs/namespace.c:1193
       task_work_run+0xc4/0x14c kernel/task_work.c:177
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       do_notify_resume+0x174/0x1f0 arch/arm64/kernel/signal.c:1127
       prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
       exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
       el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

-> #2 (&fs_info->reloc_mutex){+.+.}-{3:3}:
       __mutex_lock_common+0xd4/0xca8 kernel/locking/mutex.c:603
       __mutex_lock kernel/locking/mutex.c:747 [inline]
       mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
       btrfs_commit_transaction+0x824/0x12d8 fs/btrfs/transaction.c:2306
       btrfs_commit_super+0x84/0xa0 fs/btrfs/disk-io.c:4426
       close_ctree+0x1dc/0x60c fs/btrfs/disk-io.c:4580
       btrfs_put_super+0x20/0x30 fs/btrfs/super.c:392
       generic_shutdown_super+0x8c/0x190 fs/super.c:491
       kill_anon_super+0x24/0x44 fs/super.c:1085
       btrfs_kill_super+0x24/0x3c fs/btrfs/super.c:2440
       deactivate_locked_super+0x70/0xe8 fs/super.c:332
       deactivate_super+0xd0/0xd4 fs/super.c:363
       cleanup_mnt+0x1f8/0x234 fs/namespace.c:1186
       __cleanup_mnt+0x20/0x30 fs/namespace.c:1193
       task_work_run+0xc4/0x14c kernel/task_work.c:177
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       do_notify_resume+0x174/0x1f0 arch/arm64/kernel/signal.c:1127
       prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
       exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
       el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

-> #1 (sb_internal#2){.+.+}-{0:0}:
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1826 [inline]
       sb_start_intwrite include/linux/fs.h:1948 [inline]
       start_transaction+0x360/0x944 fs/btrfs/transaction.c:683
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:795
       btrfs_dirty_inode+0x50/0x140 fs/btrfs/inode.c:6103
       btrfs_update_time+0x1c0/0x1e8 fs/btrfs/inode.c:6145
       inode_update_time fs/inode.c:1872 [inline]
       touch_atime+0x1f0/0x4a8 fs/inode.c:1945
       file_accessed include/linux/fs.h:2516 [inline]
       btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2407
       call_mmap include/linux/fs.h:2192 [inline]
       mmap_region+0x7fc/0xc14 mm/mmap.c:1752
       do_mmap+0x644/0x97c mm/mmap.c:1540
       vm_mmap_pgoff+0xe8/0x1d0 mm/util.c:552
       ksys_mmap_pgoff+0x1cc/0x278 mm/mmap.c:1586
       __do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
       __se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
       __arm64_sys_mmap+0x58/0x6c arch/arm64/kernel/sys.c:21
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
       el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
       el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

-> #0 (&mm->mmap_lock){++++}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3095 [inline]
       check_prevs_add kernel/locking/lockdep.c:3214 [inline]
       validate_chain kernel/locking/lockdep.c:3829 [inline]
       __lock_acquire+0x1530/0x30a4 kernel/locking/lockdep.c:5053
       lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5666
       __might_fault+0x7c/0xb4 mm/memory.c:5577
       _copy_to_user include/linux/uaccess.h:134 [inline]
       copy_to_user include/linux/uaccess.h:160 [inline]
       btrfs_ioctl_get_subvol_rootref+0x3a8/0x4bc fs/btrfs/ioctl.c:3203
       btrfs_ioctl+0xa08/0xa64 fs/btrfs/ioctl.c:5556
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl fs/ioctl.c:856 [inline]
       __arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
       el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
       el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

other info that might help us debug this:

Chain exists of:
  &mm->mmap_lock --> &fs_info->reloc_mutex --> btrfs-root-00

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(btrfs-root-00);
                               lock(&fs_info->reloc_mutex);
                               lock(btrfs-root-00);
  lock(&mm->mmap_lock);

 *** DEADLOCK ***

1 lock held by syz-executor.3/1107:
 #0: ffff00011a821388 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
 #0: ffff00011a821388 (btrfs-root-00){++++}-{3:3}, at: btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
 #0: ffff00011a821388 (btrfs-root-00){++++}-{3:3}, at: btrfs_read_lock_root_node+0x13c/0x1c0 fs/btrfs/locking.c:279

stack backtrace:
CPU: 1 PID: 1107 Comm: syz-executor.3 Not tainted 6.0.0-rc7-syzkaller-18095-gbbed346d5a96 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/30/2022
Call trace:
 dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:156
 show_stack+0x2c/0x54 arch/arm64/kernel/stacktrace.c:163
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x104/0x16c lib/dump_stack.c:106
 dump_stack+0x1c/0x58 lib/dump_stack.c:113
 print_circular_bug+0x2c4/0x2c8 kernel/locking/lockdep.c:2053
 check_noncircular+0x14c/0x154 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3095 [inline]
 check_prevs_add kernel/locking/lockdep.c:3214 [inline]
 validate_chain kernel/locking/lockdep.c:3829 [inline]
 __lock_acquire+0x1530/0x30a4 kernel/locking/lockdep.c:5053
 lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5666
 __might_fault+0x7c/0xb4 mm/memory.c:5577
 _copy_to_user include/linux/uaccess.h:134 [inline]
 copy_to_user include/linux/uaccess.h:160 [inline]
 btrfs_ioctl_get_subvol_rootref+0x3a8/0x4bc fs/btrfs/ioctl.c:3203
 btrfs_ioctl+0xa08/0xa64 fs/btrfs/ioctl.c:5556
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
 el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
 el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@...glegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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