INFO: task hung in fuse_sb_destroy

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 59fc453b21f7 Merge branch 'akpm' (patches from Andrew)
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15fb2447400000
kernel config: https://syzkaller.appspot.com/x/.config?x=ea045471e4c756e8
dashboard link: https://syzkaller.appspot.com/bug?extid=6339eda9cb4ebbc4c37b
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=178a105d400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16651133400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6339ed...@syzkaller.appspotmail.com

INFO: task syz-executor221:17414 blocked for more than 140 seconds.
Not tainted 4.19.0+ #313
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor221 D23048 17414 5652 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2831 [inline]
__schedule+0x8cf/0x21d0 kernel/sched/core.c:3472
schedule+0xfe/0x460 kernel/sched/core.c:3516
fuse_wait_aborted+0x20b/0x320 fs/fuse/dev.c:2155
fuse_sb_destroy+0xe2/0x1d0 fs/fuse/inode.c:1224
fuse_kill_sb_anon+0x15/0x20 fs/fuse/inode.c:1234
deactivate_locked_super+0x97/0x100 fs/super.c:329
deactivate_super+0x2bb/0x320 fs/super.c:360
cleanup_mnt+0xbf/0x160 fs/namespace.c:1098
__cleanup_mnt+0x16/0x20 fs/namespace.c:1105
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446689
Code: e8 0c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 7b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f621e979da8 EFLAGS: 00000293 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00000000006dbc28 RCX: 0000000000446689
RDX: 0000000000446689 RSI: 000000000000000a RDI: 0000000020000180
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 00000000006dbc2c
R13: 0030656c69662f2e R14: 65646f6d746f6f72 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1009:
#0: 0000000095618e4f (rcu_read_lock){....}, at:
debug_show_all_locks+0xd0/0x424 kernel/locking/lockdep.c:4379
5 locks held by rsyslogd/5530:
#0: 0000000028bad575 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1bb/0x200
fs/file.c:766
#1: 00000000e31592cd (&rq->lock){-.-.}, at: rq_lock
kernel/sched/sched.h:1126 [inline]
#1: 00000000e31592cd (&rq->lock){-.-.}, at: __schedule+0x236/0x21d0
kernel/sched/core.c:3410
#2: 0000000095618e4f (rcu_read_lock){....}, at: trace_sched_stat_runtime
include/trace/events/sched.h:418 [inline]
#2: 0000000095618e4f (rcu_read_lock){....}, at: update_curr+0x383/0xbd0
kernel/sched/fair.c:830
#3: 00000000e31592cd (&rq->lock){-.-.}, at: rq_lock
kernel/sched/sched.h:1126 [inline]
#3: 00000000e31592cd (&rq->lock){-.-.}, at: ttwu_queue
kernel/sched/core.c:1845 [inline]
#3: 00000000e31592cd (&rq->lock){-.-.}, at: try_to_wake_up+0x9f6/0x1490
kernel/sched/core.c:2057
#4: 0000000095618e4f (rcu_read_lock){....}, at: trace_sched_stat_runtime
include/trace/events/sched.h:418 [inline]
#4: 0000000095618e4f (rcu_read_lock){....}, at: update_curr+0x383/0xbd0
kernel/sched/fair.c:830
2 locks held by getty/5620:
#0: 00000000492d5ad8 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 0000000088c4d769 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5621:
#0: 00000000ed56cf3c (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000a8112d49 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5622:
#0: 00000000858703c2 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000b20ff0f8 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5623:
#0: 00000000a0163126 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000cb4be99e (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5624:
#0: 000000006eab39a0 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000341e7ea5 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5625:
#0: 00000000e1bb9e75 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000e6c38e03 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5626:
#0: 00000000437eab2d (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000031acd5c (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by kworker/1:0/5718:
#0: 0000000003693dce ((wq_completion)"rcu_gp"){+.+.}, at:
__write_once_size include/linux/compiler.h:206 [inline]
#0: 0000000003693dce ((wq_completion)"rcu_gp"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 0000000003693dce ((wq_completion)"rcu_gp"){+.+.}, at: atomic64_set
include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 0000000003693dce ((wq_completion)"rcu_gp"){+.+.}, at: atomic_long_set
include/asm-generic/atomic-long.h:59 [inline]
#0: 0000000003693dce ((wq_completion)"rcu_gp"){+.+.}, at: set_work_data
kernel/workqueue.c:617 [inline]
#0: 0000000003693dce ((wq_completion)"rcu_gp"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 0000000003693dce ((wq_completion)"rcu_gp"){+.+.}, at:
process_one_work+0xb43/0x1c40 kernel/workqueue.c:2124
#1: 00000000fdcab2d3 ((work_completion)(&rew.rew_work)){+.+.}, at:
process_one_work+0xb9a/0x1c40 kernel/workqueue.c:2128
1 lock held by syz-executor221/17414:
#0: 000000003df3056e (&type->s_umount_key#39){+.+.}, at:
deactivate_super+0x2b3/0x320 fs/super.c:359
1 lock held by syz-executor221/18647:
#0: 00000000dd0c9ec5 (rcu_state.exp_mutex){+.+.}, at: exp_funnel_lock
kernel/rcu/tree_exp.h:296 [inline]
#0: 00000000dd0c9ec5 (rcu_state.exp_mutex){+.+.}, at:
_synchronize_rcu_expedited.constprop.58+0x7c7/0x9d0
kernel/rcu/tree_exp.h:620
1 lock held by syz-executor221/18653:
#0: 00000000dd0c9ec5 (rcu_state.exp_mutex){+.+.}, at: exp_funnel_lock
kernel/rcu/tree_exp.h:328 [inline]
#0: 00000000dd0c9ec5 (rcu_state.exp_mutex){+.+.}, at:
_synchronize_rcu_expedited.constprop.58+0x7af/0x9d0
kernel/rcu/tree_exp.h:620

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 1009 Comm: khungtaskd Not tainted 4.19.0+ #313
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
nmi_cpu_backtrace.cold.2+0x5c/0xa1 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1e8/0x22a lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:144 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xb51/0x1060 kernel/hung_task.c:289
kthread+0x35a/0x440 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:350
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 18647 Comm: syz-executor221 Not tainted 4.19.0+ #313
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:outb arch/x86/include/asm/io.h:334 [inline]
RIP: 0010:io_serial_out+0x73/0x90 drivers/tty/serial/8250/8250_port.c:455
Code: 00 49 8d 7c 24 38 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03
d3 e3 80 3c 02 00 75 19 41 03 5c 24 38 44 89 e8 89 da ee <5b> 41 5c 41 5d
5d c3 e8 e1 66 e0 fd eb c0 e8 3a 67 e0 fd eb e0 0f
RSP: 0018:ffff8801cc666f90 EFLAGS: 00000006
RAX: 0000000000000000 RBX: 00000000000003f9 RCX: 0000000000000000
RDX: 00000000000003f9 RSI: ffffffff83e257a6 RDI: ffffffff8bae5158
RBP: ffff8801cc666fa8 R08: ffff8801bf0b0600 R09: ffffed00398ccde3
R10: ffffed00398ccde3 R11: 0000000000000003 R12: ffffffff8bae5120
R13: 0000000000000000 R14: 0000000000000001 R15: ffffffff8bae5168
FS: 00007f621e97a700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f313a840000 CR3: 00000001c3654000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
serial_port_out include/linux/serial_core.h:276 [inline]
serial8250_console_write+0x34b/0xb10
drivers/tty/serial/8250/8250_port.c:3276
univ8250_console_write+0x5f/0x70 drivers/tty/serial/8250/8250_core.c:586
call_console_drivers kernel/printk/printk.c:1728 [inline]
console_unlock+0xb1f/0x1190 kernel/printk/printk.c:2414
vprintk_emit+0x391/0x990 kernel/printk/printk.c:1922
vprintk_default+0x28/0x30 kernel/printk/printk.c:1964
vprintk_func+0x7e/0x181 kernel/printk/printk_safe.c:398
printk+0xa7/0xcf kernel/printk/printk.c:1997
kobject_cleanup lib/kobject.c:638 [inline]
kobject_release lib/kobject.c:691 [inline]
kref_put include/linux/kref.h:70 [inline]
kobject_put.cold.9+0x83/0x2e4 lib/kobject.c:708
put_device drivers/base/core.c:2024 [inline]
device_unregister+0x28/0x30 drivers/base/core.c:2114
bdi_unregister+0x5ed/0x880 mm/backing-dev.c:948
release_bdi mm/backing-dev.c:964 [inline]
kref_put include/linux/kref.h:70 [inline]
bdi_put+0x153/0x180 mm/backing-dev.c:973
generic_shutdown_super+0x3c8/0x530 fs/super.c:470
kill_anon_super+0x3e/0x60 fs/super.c:1032
fuse_kill_sb_anon+0x1d/0x20 fs/fuse/inode.c:1235
deactivate_locked_super+0x97/0x100 fs/super.c:329
deactivate_super+0x2bb/0x320 fs/super.c:360
cleanup_mnt+0xbf/0x160 fs/namespace.c:1098
__cleanup_mnt+0x16/0x20 fs/namespace.c:1105
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
get_signal+0x1558/0x1980 kernel/signal.c:2347
do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446689
Code: e8 0c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 7b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f621e979da8 EFLAGS: 00000293 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00000000006dbc28 RCX: 0000000000446689
RDX: 0000000000446689 RSI: 000000000000000a RDI: 0000000020000180
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 00000000006dbc2c
R13: 0030656c69662f2e R14: 65646f6d746f6f72 R15: 0000000000000000
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.274
msecs
kobject: '0:31' (0000000050d00699): fill_kobj_path: path
= '/devices/virtual/bdi/0:31'
kobject: '0:32' (00000000d2d168d9): kobject_cleanup, parent (null)
kobject: '0:31' (0000000050d00699): kobject_cleanup, parent (null)
kobject: '0:32' (00000000d2d168d9): calling ktype release
kobject: '0:33' (00000000d76406a3): kobject_cleanup, parent (null)
kobject: '0:28' (000000002da84317): calling ktype release
kobject: '0:29' (00000000e2434e73): kobject_cleanup, parent (null)
kobject: '0:32': free name
kobject: '0:33' (00000000d76406a3): calling ktype release
kobject: '0:33': free name
kobject: '0:29' (00000000e2434e73): calling ktype release
kobject: '0:28': free name
kobject: '0:29': free name
kobject: '0:31' (0000000050d00699): calling ktype release
kobject: '0:28' (0000000080474e07): kobject_add_internal: parent: 'bdi',
set: 'devices'
kobject: '0:29' (0000000051f8f0a5): kobject_add_internal: parent: 'bdi',
set: 'devices'
kobject: '0:28' (0000000080474e07): kobject_uevent_env
kobject: '0:32' (0000000075558c25): kobject_add_internal: parent: 'bdi',
set: 'devices'
kobject: '0:33' (00000000c8dd3226): kobject_add_internal: parent: 'bdi',
set: 'devices'
kobject: '0:29' (0000000051f8f0a5): kobject_uevent_env
kobject: '0:33' (00000000c8dd3226): kobject_uevent_env
kobject: '0:31': free name
kobject: '0:28' (0000000080474e07): fill_kobj_path: path
= '/devices/virtual/bdi/0:28'
kobject: '0:29' (0000000051f8f0a5): fill_kobj_path: path
= '/devices/virtual/bdi/0:29'
kobject: '0:34' (000000008aa55f96): kobject_add_internal: parent: 'bdi',
set: 'devices'
kobject: '0:33' (00000000c8dd3226): fill_kobj_path: path
= '/devices/virtual/bdi/0:33'
kobject: '0:31' (000000008e78fdc7): kobject_add_internal: parent: 'bdi',
set: 'devices'
kobject: '0:32' (0000000075558c25): kobject_uevent_env
kobject: '0:34' (000000008aa55f96): kobject_uevent_env
kobject: '0:32' (0000000075558c25): fill_kobj_path: path
= '/devices/virtual/bdi/0:32'
kobject: '0:34' (000000008aa55f96): fill_kobj_path: path
= '/devices/virtual/bdi/0:34'


---
This bug 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 syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Dmitry Vyukov]

On Thu, Nov 1, 2018 at 11:49 AM, syzbot
<syzbot+6339ed...@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 59fc453b21f7 Merge branch 'akpm' (patches from Andrew)
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15fb2447400000
> kernel config: https://syzkaller.appspot.com/x/.config?x=ea045471e4c756e8
> dashboard link: https://syzkaller.appspot.com/bug?extid=6339eda9cb4ebbc4c37b
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=178a105d400000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16651133400000

I can easily reproduce this.

The repro gives me a task hanged at:

# cat /proc/7563/task/*/stack
[<0>] fuse_wait_aborted+0x20b/0x320
[<0>] fuse_sb_destroy+0xe2/0x1d0
[<0>] fuse_kill_sb_anon+0x15/0x20
[<0>] deactivate_locked_super+0x97/0x100
[<0>] deactivate_super+0x2bb/0x320
[<0>] cleanup_mnt+0xbf/0x160
[<0>] __cleanup_mnt+0x16/0x20
[<0>] task_work_run+0x1e8/0x2a0
[<0>] exit_to_usermode_loop+0x318/0x380
[<0>] do_syscall_64+0x6be/0x820
[<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[<0>] 0xffffffffffffffff

I double checked that writing to /sys/fs/fuse/connections/44/abort did
not help (the only entry in fuse/connections). Wrote multiple times,
and tried to kill the task, nothing helps.

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[Miklos Szeredi]

On Thu, Nov 1, 2018 at 12:05 PM, Dmitry Vyukov <dvy...@google.com> wrote:
> On Thu, Nov 1, 2018 at 11:49 AM, syzbot
> <syzbot+6339ed...@syzkaller.appspotmail.com> wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit: 59fc453b21f7 Merge branch 'akpm' (patches from Andrew)
>> git tree: upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15fb2447400000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=ea045471e4c756e8
>> dashboard link: https://syzkaller.appspot.com/bug?extid=6339eda9cb4ebbc4c37b
>> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=178a105d400000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16651133400000
>
>
> I can easily reproduce this.

I can't reproduce on my meager dual core notebook.

>
> The repro gives me a task hanged at:
>
> # cat /proc/7563/task/*/stack
> [<0>] fuse_wait_aborted+0x20b/0x320
> [<0>] fuse_sb_destroy+0xe2/0x1d0
> [<0>] fuse_kill_sb_anon+0x15/0x20
> [<0>] deactivate_locked_super+0x97/0x100
> [<0>] deactivate_super+0x2bb/0x320
> [<0>] cleanup_mnt+0xbf/0x160
> [<0>] __cleanup_mnt+0x16/0x20
> [<0>] task_work_run+0x1e8/0x2a0
> [<0>] exit_to_usermode_loop+0x318/0x380
> [<0>] do_syscall_64+0x6be/0x820
> [<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [<0>] 0xffffffffffffffff
>
> I double checked that writing to /sys/fs/fuse/connections/44/abort did
> not help (the only entry in fuse/connections). Wrote multiple times,
> and tried to kill the task, nothing helps.

What's the output of

cat /sys/fs/fuse/connections/NN/waiting

?

Thanks,
Miklos

[Miklos Szeredi]

I think I found the culprit. Does the attached patch fix it?

Thanks,
Miklos

[Dmitry Vyukov]

Hi Miklos,

I am travelling for next weeks, but you can ask syzbot to test any patches:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger
crash:

Reported-and-tested-by:
syzbot+6339ed...@syzkaller.appspotmail.com

Tested on:

commit: 651022382c7f Linux 4.20-rc1
git tree:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v4.20-rc1
kernel config: https://syzkaller.appspot.com/x/.config?x=8f559fee2fc3375a

compiler: gcc (GCC) 8.0.1 20180413 (experimental)

patch: https://syzkaller.appspot.com/x/patch.diff?x=164d714d400000

Note: testing is done by a robot and is best-effort only.

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger
crash:

Reported-and-tested-by:
syzbot+6339ed...@syzkaller.appspotmail.com

Tested on:

commit: 651022382c7f Linux 4.20-rc1
git tree:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v4.20-rc1
kernel config: https://syzkaller.appspot.com/x/.config?x=8f559fee2fc3375a
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer still triggered
crash:
INFO: task hung in fuse_sb_destroy

8021q: adding VLAN 0 to HW filter on device team0
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
INFO: task syz-executor0:8190 blocked for more than 140 seconds.
Not tainted 4.19.0+ #1

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor0 D23272 8190 5776 0x00000004

Call Trace:
context_switch kernel/sched/core.c:2831 [inline]
__schedule+0x8cf/0x21d0 kernel/sched/core.c:3472
schedule+0xfe/0x460 kernel/sched/core.c:3516
fuse_wait_aborted+0x20b/0x320 fs/fuse/dev.c:2155
fuse_sb_destroy+0xe2/0x1d0 fs/fuse/inode.c:1224
fuse_kill_sb_anon+0x15/0x20 fs/fuse/inode.c:1234
deactivate_locked_super+0x97/0x100 fs/super.c:329
deactivate_super+0x2bb/0x320 fs/super.c:360
cleanup_mnt+0xbf/0x160 fs/namespace.c:1098
__cleanup_mnt+0x16/0x20 fs/namespace.c:1105
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

RIP: 0033:0x457569
Code: Bad RIP value.
RSP: 002b:00007f1479eaec78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000002 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 000000000000000a RDI: 0000000020000180
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1479eaf6d4
R13: 00000000004c5182 R14: 00000000004d8938 R15: 00000000ffffffff

Showing all locks held in the system:

1 lock held by khungtaskd/982:
#0: 000000002c780de0 (rcu_read_lock){....}, at:
debug_show_all_locks+0xd0/0x424 kernel/locking/lockdep.c:4379
1 lock held by rsyslogd/5533:

2 locks held by getty/5623:

#0: 000000005f45ca6d (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000d283657b (&ldata->atomic_read_lock){+.+.}, at:

n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5624:

#0: 00000000b5e7910a (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000ba8a693a (&ldata->atomic_read_lock){+.+.}, at:

n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5625:

#0: 00000000e4cde13a (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000eccf3833 (&ldata->atomic_read_lock){+.+.}, at:

n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5626:

#0: 0000000000e58f8f (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000006d5d4f09 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5627:
#0: 00000000a6e021fd (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 000000000e1549c0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5628:
#0: 0000000066e7e886 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 00000000f66929ee (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
2 locks held by getty/5629:
#0: 0000000029321a0e (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:353
#1: 0000000004f1856a (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x335/0x1e80 drivers/tty/n_tty.c:2154
1 lock held by syz-executor0/8190:
#0: 00000000d6be7df4 (&type->s_umount_key#47){+.+.}, at:
deactivate_super+0x2b3/0x320 fs/super.c:359

=============================================

NMI backtrace for cpu 0

CPU: 0 PID: 982 Comm: khungtaskd Not tainted 4.19.0+ #1

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
nmi_cpu_backtrace.cold.2+0x5c/0xa1 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1e8/0x22a lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:144 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xb51/0x1060 kernel/hung_task.c:289
kthread+0x35a/0x440 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:350
Sending NMI from CPU 0 to CPUs 1:

NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0x6/0x10
arch/x86/include/asm/irqflags.h:57


Tested on:

commit: 59fc453b21f7 Merge branch 'akpm' (patches from Andrew)
git tree:

git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14d39e05400000
kernel config: https://syzkaller.appspot.com/x/.config?x=ea045471e4c756e8

[Miklos Szeredi]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
59fc453b21f7

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger
crash:

Reported-and-tested-by:
syzbot+6339ed...@syzkaller.appspotmail.com

Tested on:

commit: 59fc453b21f7 Merge branch 'akpm' (patches from Andrew)
git tree:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

kernel config: https://syzkaller.appspot.com/x/.config?x=ea045471e4c756e8
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

patch: https://syzkaller.appspot.com/x/patch.diff?x=15b6042b400000