linux-kernel - Re: [syzbot] possible deadlock in btrfs_join

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Message-ID: <000000000000bff15605ee9aa7c9@google.com>
Date:   Tue, 29 Nov 2022 03:54:50 -0800
From:   syzbot <syzbot+6eb64eace626d6222d2a@...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: Re: [syzbot] possible deadlock in btrfs_join_transaction

syzbot has found a reproducer for the following issue on:

HEAD commit:    6d464646530f 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=111da6a1880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=54b747d981acc7b7
dashboard link: https://syzkaller.appspot.com/bug?extid=6eb64eace626d6222d2a
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
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12b284bd880000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11346825880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d75f5f77b3a3/disk-6d464646.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9382f86e4d95/vmlinux-6d464646.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cf2b5f0d51dd/Image-6d464646.gz.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/6232bad1430d/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6eb64eace626d6222d2a@...kaller.appspotmail.com

BTRFS info (device loop0): using sha256 (sha256-ce) checksum algorithm
BTRFS info (device loop0): using free space tree
BTRFS info (device loop0): enabling ssd optimizations
======================================================
WARNING: possible circular locking dependency detected
6.1.0-rc6-syzkaller-32662-g6d464646530f #0 Not tainted
------------------------------------------------------
syz-executor220/3357 is trying to acquire lock:
ffff0000c9b90650 (sb_internal#2){.+.+}-{0:0}, at: btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764

but task is already holding lock:
ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0xa0/0x1d0 mm/util.c:518

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&mm->mmap_lock){++++}-{3:3}:
       __might_fault+0x7c/0xb4 mm/memory.c:5646
       _copy_to_user include/linux/uaccess.h:143 [inline]
       copy_to_user include/linux/uaccess.h:169 [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:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #4 (btrfs-root-00){++++}-{3:3}:
       down_read_nested+0x64/0x84 kernel/locking/rwsem.c:1634
       __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
       btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
       btrfs_read_lock_root_node+0x13c/0x1c0 fs/btrfs/locking.c:279
       btrfs_search_slot_get_root+0x8c/0x374 fs/btrfs/ctree.c:1665
       btrfs_search_slot+0x1dc/0x107c fs/btrfs/ctree.c:1985
       btrfs_update_root+0x6c/0x5a4 fs/btrfs/root-tree.c:132
       commit_fs_roots+0x1f0/0x33c fs/btrfs/transaction.c:1441
       btrfs_commit_transaction+0xa94/0x1574 fs/btrfs/transaction.c:2353
       btrfs_sync_fs+0x2b8/0x48c fs/btrfs/super.c:1527
       sync_filesystem+0xe0/0x134 fs/sync.c:66
       generic_shutdown_super+0x38/0x198 fs/super.c:474
       kill_anon_super+0x24/0x44 fs/super.c:1086
       btrfs_kill_super+0x24/0x3c fs/btrfs/super.c:2441
       deactivate_locked_super+0x70/0xe8 fs/super.c:332
       deactivate_super+0xd0/0xd4 fs/super.c:363
       cleanup_mnt+0x184/0x1c0 fs/namespace.c:1186
       __cleanup_mnt+0x20/0x30 fs/namespace.c:1193
       task_work_run+0x100/0x148 kernel/task_work.c:179
       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:638
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #3 (&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_record_root_in_trans fs/btrfs/transaction.c:484 [inline]
       start_transaction+0x248/0x944 fs/btrfs/transaction.c:721
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:750
       btrfs_create_common+0xf0/0x1b4 fs/btrfs/inode.c:6633
       btrfs_create+0x8c/0xb0 fs/btrfs/inode.c:6679
       lookup_open fs/namei.c:3413 [inline]
       open_last_lookups fs/namei.c:3481 [inline]
       path_openat+0x804/0x11c4 fs/namei.c:3710
       do_filp_open+0xdc/0x1b8 fs/namei.c:3740
       do_sys_openat2+0xb8/0x22c fs/open.c:1310
       do_sys_open fs/open.c:1326 [inline]
       __do_sys_openat fs/open.c:1342 [inline]
       __se_sys_openat fs/open.c:1337 [inline]
       __arm64_sys_openat+0xb0/0xe0 fs/open.c:1337
       __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:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #2 (btrfs_trans_num_extwriters){++++}-{0:0}:
       join_transaction+0x10c/0x65c fs/btrfs/transaction.c:299
       start_transaction+0x460/0x944 fs/btrfs/transaction.c:658
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:750
       btrfs_create_common+0xf0/0x1b4 fs/btrfs/inode.c:6633
       btrfs_create+0x8c/0xb0 fs/btrfs/inode.c:6679
       lookup_open fs/namei.c:3413 [inline]
       open_last_lookups fs/namei.c:3481 [inline]
       path_openat+0x804/0x11c4 fs/namei.c:3710
       do_filp_open+0xdc/0x1b8 fs/namei.c:3740
       do_sys_openat2+0xb8/0x22c fs/open.c:1310
       do_sys_open fs/open.c:1326 [inline]
       __do_sys_openat fs/open.c:1342 [inline]
       __se_sys_openat fs/open.c:1337 [inline]
       __arm64_sys_openat+0xb0/0xe0 fs/open.c:1337
       __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:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #1 (btrfs_trans_num_writers){++++}-{0:0}:
       join_transaction+0xe8/0x65c fs/btrfs/transaction.c:298
       start_transaction+0x460/0x944 fs/btrfs/transaction.c:658
       btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:750
       btrfs_create_common+0xf0/0x1b4 fs/btrfs/inode.c:6633
       btrfs_create+0x8c/0xb0 fs/btrfs/inode.c:6679
       lookup_open fs/namei.c:3413 [inline]
       open_last_lookups fs/namei.c:3481 [inline]
       path_openat+0x804/0x11c4 fs/namei.c:3710
       do_filp_open+0xdc/0x1b8 fs/namei.c:3740
       do_sys_openat2+0xb8/0x22c fs/open.c:1310
       do_sys_open fs/open.c:1326 [inline]
       __do_sys_openat fs/open.c:1342 [inline]
       __se_sys_openat fs/open.c:1337 [inline]
       __arm64_sys_openat+0xb0/0xe0 fs/open.c:1337
       __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:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #0 (sb_internal#2){.+.+}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3097 [inline]
       check_prevs_add kernel/locking/lockdep.c:3216 [inline]
       validate_chain kernel/locking/lockdep.c:3831 [inline]
       __lock_acquire+0x1530/0x3084 kernel/locking/lockdep.c:5055
       lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5668
       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:652
       btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
       btrfs_dirty_inode+0x4c/0x13c fs/btrfs/inode.c:6085
       btrfs_update_time+0x120/0x138 fs/btrfs/inode.c:6127
       inode_update_time fs/inode.c:1871 [inline]
       touch_atime+0x1f0/0x4a8 fs/inode.c:1944
       file_accessed include/linux/fs.h:2521 [inline]
       btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2333
       call_mmap include/linux/fs.h:2196 [inline]
       mmap_region+0x8a0/0x1064 mm/mmap.c:2625
       do_mmap+0x6e8/0xa30 mm/mmap.c:1412
       vm_mmap_pgoff+0xe8/0x1d0 mm/util.c:520
       ksys_mmap_pgoff+0x1cc/0x278 mm/mmap.c:1458
       __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:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

Chain exists of:
  sb_internal#2 --> btrfs-root-00 --> &mm->mmap_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&mm->mmap_lock);
                               lock(btrfs-root-00);
                               lock(&mm->mmap_lock);
  lock(sb_internal#2);

 *** DEADLOCK ***

2 locks held by syz-executor220/3357:
 #0: ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff0000ca11fb08 (&mm->mmap_lock){++++}-{3:3}, at: vm_mmap_pgoff+0xa0/0x1d0 mm/util.c:518
 #1: ffff0000c9b90460 (sb_writers#8){.+.+}-{0:0}, at: file_accessed include/linux/fs.h:2521 [inline]
 #1: ffff0000c9b90460 (sb_writers#8){.+.+}-{0:0}, at: btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2333

stack backtrace:
CPU: 1 PID: 3357 Comm: syz-executor220 Not tainted 6.1.0-rc6-syzkaller-32662-g6d464646530f #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:2055
 check_noncircular+0x14c/0x154 kernel/locking/lockdep.c:2177
 check_prev_add kernel/locking/lockdep.c:3097 [inline]
 check_prevs_add kernel/locking/lockdep.c:3216 [inline]
 validate_chain kernel/locking/lockdep.c:3831 [inline]
 __lock_acquire+0x1530/0x3084 kernel/locking/lockdep.c:5055
 lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5668
 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:652
 btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:764
 btrfs_dirty_inode+0x4c/0x13c fs/btrfs/inode.c:6085
 btrfs_update_time+0x120/0x138 fs/btrfs/inode.c:6127
 inode_update_time fs/inode.c:1871 [inline]
 touch_atime+0x1f0/0x4a8 fs/inode.c:1944
 file_accessed include/linux/fs.h:2521 [inline]
 btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2333
 call_mmap include/linux/fs.h:2196 [inline]
 mmap_region+0x8a0/0x1064 mm/mmap.c:2625
 do_mmap+0x6e8/0xa30 mm/mmap.c:1412
 vm_mmap_pgoff+0xe8/0x1d0 mm/util.c:520
 ksys_mmap_pgoff+0x1cc/0x278 mm/mmap.c:1458
 __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:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584