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SubjectRe: INFO: task hung in lock_mount
From
syzbot has found a reproducer for the following crash on:

HEAD commit: a048a07d7f45 powerpc/64s: Add support for a store forwardi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1084cc27800000
kernel config: https://syzkaller.appspot.com/x/.config?x=982e2df1b9e60b02
dashboard link: https://syzkaller.appspot.com/bug?extid=221d75710bde87fa0e97
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13992a0f800000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=131a727b800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+221d75710bde87fa0e97@syzkaller.appspotmail.com

INFO: task syz-executor694:4903 blocked for more than 120 seconds.
Not tainted 4.17.0-rc6+ #63
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor694 D24936 4903 4506 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2859 [inline]
__schedule+0x801/0x1e30 kernel/sched/core.c:3501
schedule+0xef/0x430 kernel/sched/core.c:3545
__rwsem_down_write_failed_common+0x919/0x15d0
kernel/locking/rwsem-xadd.c:565
rwsem_down_write_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:594
call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:117
__down_write arch/x86/include/asm/rwsem.h:142 [inline]
down_write+0xa2/0x120 kernel/locking/rwsem.c:72
namespace_lock fs/namespace.c:1431 [inline]
lock_mount+0xdc/0x2e0 fs/namespace.c:2093
do_loopback fs/namespace.c:2221 [inline]
do_mount+0xebc/0x3070 fs/namespace.c:2842
ksys_mount+0x12d/0x140 fs/namespace.c:3064
__do_sys_mount fs/namespace.c:3078 [inline]
__se_sys_mount fs/namespace.c:3075 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x447099
RSP: 002b:00007f0d700b4da8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00000000006ddcb4 RCX: 0000000000447099
RDX: 0000000020000140 RSI: 00000000200000c0 RDI: 0000000020000000
RBP: 00000000006ddcb0 R08: 0000000020000200 R09: 0000000000000000
R10: 0000000000003080 R11: 0000000000000246 R12: 0030656c69662f2e
R13: 6f7365725f736e64 R14: 70756f7267632f2e R15: 0000000000000007

Showing all locks held in the system:
2 locks held by khungtaskd/892:
#0: (ptrval) (rcu_read_lock){....}, at:
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: (ptrval) (rcu_read_lock){....}, at: watchdog+0x1ff/0xf60
kernel/hung_task.c:249
#1: (ptrval) (tasklist_lock){.+.+}, at:
debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
1 lock held by rsyslogd/4380:
#0: (ptrval) (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x1a9/0x1e0
fs/file.c:766
2 locks held by getty/4470:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4471:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4472:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4473:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4474:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4475:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4476:
#0: (ptrval) (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (ptrval) (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by syz-executor694/4903:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4901:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4905:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4911:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4913:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4919:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4921:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4928:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4935:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4937:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4939:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
2 locks held by syz-executor694/4941:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
#1: (ptrval) (namespace_sem){++++}, at: namespace_lock
fs/namespace.c:1431 [inline]
#1: (ptrval) (namespace_sem){++++}, at: lock_mount+0xdc/0x2e0
fs/namespace.c:2093
1 lock held by syz-executor694/4943:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
inode_lock_shared include/linux/fs.h:723 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lookup_slow+0x49/0x80 fs/namei.c:1646
2 locks held by syz-executor694/4944:
#0: (ptrval) (sb_writers#12){.+.+}, at: sb_start_write
include/linux/fs.h:1550 [inline]
#0: (ptrval) (sb_writers#12){.+.+}, at: mnt_want_write+0x3f/0xc0
fs/namespace.c:386
#1: (ptrval) (&sb->s_type->i_mutex_key#15/1){+.+.}, at:
inode_lock_nested include/linux/fs.h:748 [inline]
#1: (ptrval) (&sb->s_type->i_mutex_key#15/1){+.+.}, at:
filename_create+0x1aa/0x5a0 fs/namei.c:3606
1 lock held by syz-executor694/4945:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088
1 lock held by syz-executor694/4947:
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at: inode_lock
include/linux/fs.h:713 [inline]
#0: (ptrval) (&sb->s_type->i_mutex_key#15){++++}, at:
lock_mount+0x8c/0x2e0 fs/namespace.c:2088

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

NMI backtrace for cpu 0
CPU: 0 PID: 892 Comm: khungtaskd Not tainted 4.17.0-rc6+ #63
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+0x1b9/0x294 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x151/0x192 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:138 [inline]
check_hung_task kernel/hung_task.c:132 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
watchdog+0xc10/0xf60 kernel/hung_task.c:249
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4901 Comm: syz-executor694 Not tainted 4.17.0-rc6+ #63
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:__lock_release kernel/locking/lockdep.c:3674 [inline]
RIP: 0010:lock_release+0x1f5/0xa10 kernel/locking/lockdep.c:3939
RSP: 0018:ffff8801afca7708 EFLAGS: 00000097
RAX: 0000000000000003 RBX: 1ffff10035f94ee6 RCX: ffffffff815e1551
RDX: 0000000000000004 RSI: 0000000000000001 RDI: 0000000000000001
RBP: ffff8801afca7838 R08: 0000000000000000 R09: ffffed00351966c8
R10: ffffed00351966c8 R11: ffff8801a8cb3643 R12: ffff8801afca7810
R13: ffff8801a8cb3658 R14: ffff8801a9a003c0 R15: ffff8801afca7750
FS: 00007f0d700f7700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 00000001d05cc000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__raw_spin_unlock include/linux/spinlock_api_smp.h:150 [inline]
_raw_spin_unlock+0x1a/0x30 kernel/locking/spinlock.c:176
spin_unlock include/linux/spinlock.h:350 [inline]
lockref_get+0x42/0x50 lib/lockref.c:51
dget include/linux/dcache.h:326 [inline]
mnt_set_mountpoint+0xe7/0x360 fs/namespace.c:914
propagate_one+0x5a7/0x910 fs/pnode.c:269
propagate_mnt+0x18a/0x3e0 fs/pnode.c:315
attach_recursive_mnt+0x5f8/0xb50 fs/namespace.c:2033
graft_tree+0x1aa/0x240 fs/namespace.c:2133
do_add_mount+0x1fe/0x370 fs/namespace.c:2491
do_new_mount fs/namespace.c:2532 [inline]
do_mount+0x18e6/0x3070 fs/namespace.c:2848
ksys_mount+0x12d/0x140 fs/namespace.c:3064
__do_sys_mount fs/namespace.c:3078 [inline]
__se_sys_mount fs/namespace.c:3075 [inline]
__x64_sys_mount+0xbe/0x150 fs/namespace.c:3075
do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x447099
RSP: 002b:00007f0d700f6da8 EFLAGS: 00000293 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00000000006ddc84 RCX: 0000000000447099
RDX: 00000000200001c0 RSI: 0000000020026ff8 RDI: 000000002000a000
RBP: 00000000006ddc80 R08: 00000000200007c0 R09: 0000000000000000
R10: 0000000000000080 R11: 0000000000000293 R12: 0030656c69662f2e
R13: 6f7365725f736e64 R14: 70756f7267632f2e R15: 0000000000000007
Code: c1 ea 03 0f b6 14 02 48 89 f8 83 e0 07 83 c0 03 65 4c 8b 34 25 40 ee
01 00 38 d0 7c 08 84 d2 0f 85 67 06 00 00 8b 3d fb bd ac 07 <85> ff 0f 84
41 02 00 00 49 8d 86 30 08 00 00 48 89 c2 48 89 85

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