Re: [syzbot] [btrfs?] INFO: task hung in btrfs_sync_file (2)

[Dmitry Vyukov]

On Tue, 6 Jun 2023 at 16:30, David Sterba <dsterba@xxxxxxx> wrote:
>
> On Thu, Jun 01, 2023 at 06:15:06PM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    715abedee4cd Add linux-next specific files for 20230515
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=16cc8ced280000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=6a2745d066dda0ec
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a694851c6ab28cbcfb9c
> > compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=146e7c35280000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12ea7ffe280000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/d4d1d06b34b8/disk-715abede.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/3ef33a86fdc8/vmlinux-715abede.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/e0006b413ed1/bzImage-715abede.xz
> > mounted in repro: https://storage.googleapis.com/syzbot-assets/8a4c583d7fb5/mount_0.gz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+a694851c6ab28cbcfb9c@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > INFO: task syz-executor274:6164 blocked for more than 143 seconds.
>
> 143+ seconds in a lock might be a lot, but this is file sync and the
> the system could be overloaded.
>
> >       Not tainted 6.4.0-rc2-next-20230515-syzkaller #0
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > task:syz-executor274 state:D stack:24920 pid:6164  ppid:5041   flags:0x00004004
> > Call Trace:
> >  <TASK>
> >  context_switch kernel/sched/core.c:5343 [inline]
> >  __schedule+0x1d15/0x5790 kernel/sched/core.c:6669
> >  schedule+0xde/0x1a0 kernel/sched/core.c:6745
> >  schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6804
> >  rwsem_down_write_slowpath+0x3e2/0x1220 kernel/locking/rwsem.c:1178
> >  __down_write_common kernel/locking/rwsem.c:1306 [inline]
> >  __down_write kernel/locking/rwsem.c:1315 [inline]
> >  down_write+0x1d2/0x200 kernel/locking/rwsem.c:1574
> >  inode_lock include/linux/fs.h:775 [inline]
>
> Inode lock
>
> >  btrfs_inode_lock+0x7e/0xf0 fs/btrfs/inode.c:377
> >  btrfs_sync_file+0x455/0x12d0 fs/btrfs/file.c:1808
> >  vfs_fsync_range+0x13e/0x230 fs/sync.c:188
> >  generic_write_sync include/linux/fs.h:2469 [inline]
> >  btrfs_do_write_iter+0x520/0x1210 fs/btrfs/file.c:1680
> >  call_write_iter include/linux/fs.h:1868 [inline]
> >  new_sync_write fs/read_write.c:491 [inline]
> >  vfs_write+0x945/0xd50 fs/read_write.c:584
> >  ksys_write+0x12b/0x250 fs/read_write.c:637
> >  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >  do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x7f0de39026c9
> > RSP: 002b:00007f0de38a5208 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> > RAX: ffffffffffffffda RBX: 00007f0de3984788 RCX: 00007f0de39026c9
> > RDX: 0000000000000128 RSI: 0000000020004400 RDI: 0000000000000006
> > RBP: 00007f0de3984780 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0de398478c
> > R13: 00007fffb0c5635f R14: 00007f0de38a5300 R15: 0000000000022000
> >  </TASK>
> > INFO: task syz-executor274:6181 blocked for more than 143 seconds.
> >       Not tainted 6.4.0-rc2-next-20230515-syzkaller #0
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > task:syz-executor274 state:D stack:26416 pid:6181  ppid:5041   flags:0x00004004
> > Call Trace:
> >  <TASK>
> >  context_switch kernel/sched/core.c:5343 [inline]
> >  __schedule+0x1d15/0x5790 kernel/sched/core.c:6669
> >  schedule+0xde/0x1a0 kernel/sched/core.c:6745
> >  wait_on_state fs/btrfs/extent-io-tree.c:707 [inline]
> >  wait_extent_bit+0x56e/0x670 fs/btrfs/extent-io-tree.c:751
> >  lock_extent+0x120/0x1c0 fs/btrfs/extent-io-tree.c:1742
> >  btrfs_page_mkwrite+0x652/0x11a0 fs/btrfs/inode.c:8336
> >  do_page_mkwrite+0x1a1/0x690 mm/memory.c:2934
> >  wp_page_shared mm/memory.c:3283 [inline]
> >  do_wp_page+0x356/0x34e0 mm/memory.c:3365
> >  handle_pte_fault mm/memory.c:4967 [inline]
> >  __handle_mm_fault+0x1635/0x4170 mm/memory.c:5092
> >  handle_mm_fault+0x2af/0x9f0 mm/memory.c:5246
> >  do_user_addr_fault+0x51a/0x1210 arch/x86/mm/fault.c:1440
> >  handle_page_fault arch/x86/mm/fault.c:1534 [inline]
> >  exc_page_fault+0x98/0x170 arch/x86/mm/fault.c:1590
> >  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:570
> > RIP: 0010:rep_movs_alternative+0x33/0xb0 arch/x86/lib/copy_user_64.S:56
> > Code: 46 83 f9 08 73 21 85 c9 74 0f 8a 06 88 07 48 ff c7 48 ff c6 48 ff c9 75 f1 c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 8b 06 <48> 89 07 48 83 c6 08 48 83 c7 08 83 e9 08 74 df 83 f9 08 73 e8 eb
> > RSP: 0018:ffffc9000becf728 EFLAGS: 00050206
> > RAX: 0000000000000000 RBX: 0000000000000038 RCX: 0000000000000038
> > RDX: fffff520017d9efb RSI: ffffc9000becf7a0 RDI: 0000000020000120
> > RBP: 0000000020000120 R08: 0000000000000000 R09: fffff520017d9efa
> > R10: ffffc9000becf7d7 R11: 0000000000000001 R12: ffffc9000becf7a0
> > R13: 0000000020000158 R14: 0000000000000000 R15: ffffc9000becf7a0
> >  copy_user_generic arch/x86/include/asm/uaccess_64.h:112 [inline]
> >  raw_copy_to_user arch/x86/include/asm/uaccess_64.h:133 [inline]
> >  _copy_to_user lib/usercopy.c:41 [inline]
> >  _copy_to_user+0xab/0xc0 lib/usercopy.c:34
> >  copy_to_user include/linux/uaccess.h:191 [inline]
> >  fiemap_fill_next_extent+0x217/0x370 fs/ioctl.c:144
> >  emit_fiemap_extent+0x18e/0x380 fs/btrfs/extent_io.c:2616
> >  fiemap_process_hole+0x516/0x610 fs/btrfs/extent_io.c:2874
>
> and extent enumeration from FIEMAP, this would qualify as a stress on
> the inode
>
> >  extent_fiemap+0x123b/0x1950 fs/btrfs/extent_io.c:3089
> >  btrfs_fiemap+0xe9/0x170 fs/btrfs/inode.c:8008
> >  ioctl_fiemap fs/ioctl.c:219 [inline]
> >  do_vfs_ioctl+0x466/0x1670 fs/ioctl.c:810
> >  __do_sys_ioctl fs/ioctl.c:868 [inline]
> >  __se_sys_ioctl fs/ioctl.c:856 [inline]
> >  __x64_sys_ioctl+0x10c/0x210 fs/ioctl.c:856
> >  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >  do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
> >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x7f0de39026c9
> > RSP: 002b:00007f0ddc484208 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 00007f0de3984798 RCX: 00007f0de39026c9
> > RDX: 0000000020000100 RSI: 00000000c020660b RDI: 0000000000000005
> > RBP: 00007f0de3984790 R08: 00007f0ddc484700 R09: 0000000000000000
> > R10: 00007f0ddc484700 R11: 0000000000000246 R12: 00007f0de398479c
> > R13: 00007fffb0c5635f R14: 00007f0ddc484300 R15: 0000000000022000
> >  </TASK>
> >
> > 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@xxxxxxxxxxxxxxxx.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> >
> > If the bug is already fixed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
>
> I was not able to decipher from the reproducer what exactly is the
> workload, there are some writes, there's one ioctl called by number
> (syscall(__NR_ioctl, r[0], 0xc020660b, 0x20000100ul)), no sync or fsync
> so they're implicit.
>
> This seems to be an 'invalid' report, the system is overloaded. There
> are several other reports stuck in fsync() with the same time out. IIRC
> the default is 300 so perhaps the syzkaller can be updated not to
> trigger too early.

Hi David,

I've just tried on the latest kernel and the default seems to be 120:

$ make defconfig
$ scripts/config -e DETECT_HUNG_TASK
$ make olddefconfig
$ grep HUNG .config
CONFIG_DEFAULT_HUNG_TASK_TIMEOUT=120

I assumed uninterruptible sleeps should be limited to O(seconds) at most, no?