INFO: task hung in lock_mount

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: a844dc4c Linux 4.14.158
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13e80232e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c02bef505ffc02ff
dashboard link: https://syzkaller.appspot.com/bug?extid=be9f2215577e0744f2e5
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+be9f22...@syzkaller.appspotmail.com

team0 (unregistering): Port device team_slave_0 removed
bond0 (unregistering): Releasing backup interface bond_slave_1
bond0 (unregistering): Releasing backup interface bond_slave_0
bond0 (unregistering): Released all slaves
INFO: task syz-executor.5:13683 blocked for more than 140 seconds.
Not tainted 4.14.158-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.5 D28496 13683 6958 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
schedule+0x92/0x1c0 kernel/sched/core.c:3428
__rwsem_down_write_failed_common kernel/locking/rwsem-xadd.c:588 [inline]
rwsem_down_write_failed+0x5ce/0xb50 kernel/locking/rwsem-xadd.c:617
call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:105
__down_write arch/x86/include/asm/rwsem.h:126 [inline]
down_write+0x53/0x90 kernel/locking/rwsem.c:56
inode_lock include/linux/fs.h:718 [inline]
lock_mount+0x8c/0x2c0 fs/namespace.c:2119
do_add_mount+0x27/0x350 fs/namespace.c:2496
do_new_mount fs/namespace.c:2563 [inline]
do_mount+0x1307/0x27d0 fs/namespace.c:2879
SYSC_mount fs/namespace.c:3095 [inline]
SyS_mount+0xab/0x120 fs/namespace.c:3072
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x45a6f9
RSP: 002b:00007f504e5d0c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 000000000045a6f9
RDX: 00000000200008c0 RSI: 0000000020000000 RDI: 0000000000000000
RBP: 000000000075bfc8 R08: 0000000020000800 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f504e5d16d4
R13: 00000000004c7aa2 R14: 00000000004de940 R15: 00000000ffffffff
INFO: task syz-executor.5:13684 blocked for more than 140 seconds.
Not tainted 4.14.158-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.5 D29296 13684 6958 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
schedule+0x92/0x1c0 kernel/sched/core.c:3428
__rwsem_down_write_failed_common kernel/locking/rwsem-xadd.c:588 [inline]
rwsem_down_write_failed+0x5ce/0xb50 kernel/locking/rwsem-xadd.c:617
call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:105
__down_write arch/x86/include/asm/rwsem.h:126 [inline]
down_write+0x53/0x90 kernel/locking/rwsem.c:56
inode_lock include/linux/fs.h:718 [inline]
do_last fs/namei.c:3328 [inline]
path_openat+0xfab/0x3f70 fs/namei.c:3566
do_filp_open+0x18e/0x250 fs/namei.c:3600
do_sys_open+0x2c5/0x430 fs/open.c:1084
SYSC_open fs/open.c:1102 [inline]
SyS_open fs/open.c:1097 [inline]
SYSC_creat fs/open.c:1142 [inline]
SyS_creat+0x27/0x30 fs/open.c:1140
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x45a6f9
RSP: 002b:00007f504e5afc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 000000000045a6f9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000300
RBP: 000000000075c070 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f504e5b06d4
R13: 00000000004c0fa8 R14: 00000000004d4da0 R15: 00000000ffffffff

Showing all locks held in the system:
1 lock held by khungtaskd/1036:
#0: (tasklist_lock){.+.+}, at: [<ffffffff8148c8a8>]
debug_show_all_locks+0x7f/0x21f kernel/locking/lockdep.c:4544
1 lock held by rsyslogd/6787:
#0: (&f->f_pos_lock){+.+.}, at: [<ffffffff81966a1b>]
__fdget_pos+0xab/0xd0 fs/file.c:769
2 locks held by getty/6909:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6910:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6911:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6912:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6913:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6914:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/6915:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by syz-executor.5/13646:
#0: (sb_writers#14){.+.+}, at: [<ffffffff8196fd1f>] sb_start_write
include/linux/fs.h:1548 [inline]
#0: (sb_writers#14){.+.+}, at: [<ffffffff8196fd1f>]
mnt_want_write+0x3f/0xb0 fs/namespace.c:386
#1: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8192ebfb>]
inode_lock include/linux/fs.h:718 [inline]
#1: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8192ebfb>] do_last
fs/namei.c:3328 [inline]
#1: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8192ebfb>]
path_openat+0xfab/0x3f70 fs/namei.c:3566
1 lock held by syz-executor.5/13683:
#0: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8197150c>]
inode_lock include/linux/fs.h:718 [inline]
#0: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8197150c>]
lock_mount+0x8c/0x2c0 fs/namespace.c:2119
2 locks held by syz-executor.5/13684:
#0: (sb_writers#14){.+.+}, at: [<ffffffff8196fd1f>] sb_start_write
include/linux/fs.h:1548 [inline]
#0: (sb_writers#14){.+.+}, at: [<ffffffff8196fd1f>]
mnt_want_write+0x3f/0xb0 fs/namespace.c:386
#1: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8192ebfb>]
inode_lock include/linux/fs.h:718 [inline]
#1: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8192ebfb>] do_last
fs/namei.c:3328 [inline]
#1: (&sb->s_type->i_mutex_key#21){++++}, at: [<ffffffff8192ebfb>]
path_openat+0xfab/0x3f70 fs/namei.c:3566

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

NMI backtrace for cpu 0
CPU: 0 PID: 1036 Comm: khungtaskd Not tainted 4.14.158-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x142/0x197 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x94 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x141/0x189 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:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5e7/0xb90 kernel/hung_task.c:274
kthread+0x319/0x430 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff866554ae


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.