INFO: task hung in lookup_slow

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
b5dbc28762fd3fd40ba76303be0c7f707826f982 (Sat Mar 31 04:53:57 2018 +0000)
Merge tag 'kbuild-fixes-v4.16-3' of
git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=c7f5a6b798135cb8c7a9

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=6203555526475776
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
compiler: gcc (GCC) 7.1.1 20170620
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org
vi...@zeniv.linux.org.uk]

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c7f5a6...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
INFO: task syz-executor0:24259 blocked for more than 120 seconds.
__find_get_block_slow() failed. block=1, b_blocknr=8
Not tainted 4.16.0-rc7+ #8
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
b_state=0x00000029, b_size=512
syz-executor0 D25296 24259 4520 0x00000004
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
Call Trace:
context_switch kernel/sched/core.c:2862 [inline]
__schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
schedule+0xf5/0x430 kernel/sched/core.c:3499
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__rwsem_down_read_failed_common kernel/locking/rwsem-xadd.c:269 [inline]
rwsem_down_read_failed+0x401/0x6e0 kernel/locking/rwsem-xadd.c:286
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
call_rwsem_down_read_failed+0x18/0x30 arch/x86/lib/rwsem.S:94
__down_read arch/x86/include/asm/rwsem.h:83 [inline]
down_read+0xa4/0x150 kernel/locking/rwsem.c:26
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
inode_lock_shared include/linux/fs.h:723 [inline]
lookup_slow+0x18e/0x4d0 fs/namei.c:1612
__find_get_block_slow() failed. block=1, b_blocknr=8
walk_component+0x89f/0x13d0 fs/namei.c:1763
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
lookup_last fs/namei.c:2231 [inline]
path_lookupat+0x1d7/0xba0 fs/namei.c:2281
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
filename_lookup+0x25f/0x500 fs/namei.c:2315
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
user_path_at_empty+0x40/0x50 fs/namei.c:2569
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
user_path_at include/linux/namei.h:57 [inline]
vfs_statx+0xe9/0x190 fs/stat.c:185
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
vfs_lstat include/linux/fs.h:3080 [inline]
SYSC_newlstat+0x87/0xf0 fs/stat.c:350
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
SyS_newlstat+0x1d/0x30 fs/stat.c:344
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x454e79
__find_get_block_slow() failed. block=1, b_blocknr=8
RSP: 002b:00007f4670a0ec68 EFLAGS: 00000246 ORIG_RAX: 0000000000000006
RAX: ffffffffffffffda RBX: 00007f4670a0f6d4 RCX: 0000000000454e79
RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000020000140
RBP: 000000000072bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
R13: 00000000000003e3 R14: 00000000006f7de8 R15: 0000000000000001

Showing all locks held in the system:
__find_get_block_slow() failed. block=1, b_blocknr=8
2 locks held by khungtaskd/873:
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
__find_get_block_slow() failed. block=1, b_blocknr=8
#0: (rcu_read_lock){....}, at: [<0000000027ddb5b4>]
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: (rcu_read_lock){....}, at: [<0000000027ddb5b4>] watchdog+0x1c5/0xd60
kernel/hung_task.c:249
#1: (tasklist_lock){.+.+}, at: [<0000000062d24e0a>]
debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
1 lock held by rsyslogd/4355:
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
#0: (&f->f_pos_lock){+.+.}
__find_get_block_slow() failed. block=1, b_blocknr=8
, at: [<000000005c949610>] __fdget_pos+0x12b/0x190 fs/file.c:765
2 locks held by getty/4446:
#0: (&tty->ldisc_sem){++++}, at: [<00000000d4128005>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002f338317>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4447:
#0: (&tty->ldisc_sem){++++}, at: [<00000000d4128005>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002f338317>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4448:
#0: (&tty->ldisc_sem){++++}, at: [<00000000d4128005>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002f338317>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4449:
#0: (&tty->ldisc_sem){++++}
b_state=0x00000029, b_size=512
, at: [<00000000d4128005>] ldsem_down_read+0x37/0x40
drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002f338317>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4450:
device loop0 blocksize: 4096
#0: (&tty->ldisc_sem){++++}
__find_get_block_slow() failed. block=1, b_blocknr=8
, at: [<00000000d4128005>] ldsem_down_read+0x37/0x40
drivers/tty/tty_ldsem.c:365
#1: (
b_state=0x00000029, b_size=512
&ldata->atomic_read_lock){+.+.}, at: [<000000002f338317>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4451:
#0:
device loop0 blocksize: 4096
(&tty->ldisc_sem){++++}
__find_get_block_slow() failed. block=1, b_blocknr=8
, at: [<00000000d4128005>] ldsem_down_read+0x37/0x40
drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}
b_state=0x00000029, b_size=512
, at: [<000000002f338317>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4452:
#0:
device loop0 blocksize: 4096
(&tty->ldisc_sem){++++}, at: [<00000000d4128005>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
__find_get_block_slow() failed. block=1, b_blocknr=8
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000002f338317>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
1 lock held by syz-executor0/24259:
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
#0: (&sb->s_type->i_mutex_key#14
__find_get_block_slow() failed. block=1, b_blocknr=8
){++++}, at: [<0000000053b65d89>] inode_lock_shared include/linux/fs.h:723
[inline]
){++++}, at: [<0000000053b65d89>] lookup_slow+0x18e/0x4d0 fs/namei.c:1612

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

b_state=0x00000029, b_size=512
NMI backtrace for cpu 0
CPU: 0 PID: 873 Comm: khungtaskd Not tainted 4.16.0-rc7+ #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
device loop0 blocksize: 4096
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x123/0x180 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
__find_get_block_slow() failed. block=1, b_blocknr=8
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+0x90c/0xd60 kernel/hung_task.c:249
b_state=0x00000029, b_size=512
device loop0 blocksize: 4096
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Sending NMI from CPU 0 to CPUs 1:
__find_get_block_slow() failed. block=1, b_blocknr=8
NMI backtrace for cpu 1
CPU: 1 PID: 24240 Comm: syz-executor0 Not tainted 4.16.0-rc7+ #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:arch_local_save_flags arch/x86/include/asm/paravirt.h:773 [inline]
RIP: 0010:arch_local_irq_save arch/x86/include/asm/paravirt.h:795 [inline]
RIP: 0010:lock_acquire+0xe6/0x580 kernel/locking/lockdep.c:3915
RSP: 0018:ffff8801db107470 EFLAGS: 00000046
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 1ffffffff10a24ec RSI: 0000000000000000 RDI: ffffffff88512760
RBP: ffff8801db107568 R08: 0000000000000001 R09: 0000000000000000
R10: 1ffff1003b620e94 R11: 0000000000000020 R12: 1ffff1003b620e94
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000001
FS: 00007f4670a30700(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffff600400 CR3: 00000001cac77001 CR4: 00000000001606e0
DR0: 0000000020000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x96/0xc0 kernel/locking/spinlock.c:152
try_to_wake_up+0xbc/0x15f0 kernel/sched/core.c:1989
wake_up_process+0x10/0x20 kernel/sched/core.c:2152
process_timeout+0x31/0x40 kernel/time/timer.c:1730
call_timer_fn+0x228/0x820 kernel/time/timer.c:1326
expire_timers kernel/time/timer.c:1363 [inline]
__run_timers+0x7ee/0xb70 kernel/time/timer.c:1666
run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
__do_softirq+0x2d7/0xb85 kernel/softirq.c:285
invoke_softirq kernel/softirq.c:365 [inline]
irq_exit+0x1cc/0x200 kernel/softirq.c:405
exiting_irq arch/x86/include/asm/apic.h:541 [inline]
smp_apic_timer_interrupt+0x16b/0x700 arch/x86/kernel/apic/apic.c:1052
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:857
</IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:778
[inline]
RIP: 0010:console_trylock_spinning kernel/printk/printk.c:1678 [inline]
RIP: 0010:vprintk_emit+0xa68/0xb90 kernel/printk/printk.c:1906
RSP: 0018:ffff8801cabf7000 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff12
RAX: 0000000000040000 RBX: 1ffffffff10a24ed RCX: ffffffff815ae4cf
RDX: 0000000000040000 RSI: ffffc90001eb0000 RDI: 0000000000000246
RBP: ffff8801cabf7188 R08: 1ffff1003957edce R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000034
R13: ffff8801cabf70e0 R14: ffffed003957ee1c R15: ffffffff89db2f40
vprintk_default+0x28/0x30 kernel/printk/printk.c:1947
vprintk_func+0x57/0xc0 kernel/printk/printk_safe.c:379
printk+0xaa/0xca kernel/printk/printk.c:1980
__find_get_block_slow fs/buffer.c:232 [inline]
__find_get_block+0xc95/0xd90 fs/buffer.c:1310
__getblk_slow fs/buffer.c:1055 [inline]
__getblk_gfp+0x26c/0xb80 fs/buffer.c:1336
__bread_gfp+0x2d/0x290 fs/buffer.c:1370
sb_bread include/linux/buffer_head.h:309 [inline]
fat__get_entry+0x195/0x910 fs/fat/dir.c:101
fat_get_entry fs/fat/dir.c:129 [inline]
fat_search_long+0x32f/0x14b0 fs/fat/dir.c:477
vfat_find+0x134/0x180 fs/fat/namei_vfat.c:697
vfat_lookup+0xf3/0x750 fs/fat/namei_vfat.c:720
lookup_real fs/namei.c:1493 [inline]
__lookup_hash+0x117/0x190 fs/namei.c:1513
filename_create+0x1c7/0x520 fs/namei.c:3626
user_path_create fs/namei.c:3683 [inline]
SYSC_mkdirat fs/namei.c:3815 [inline]
SyS_mkdirat fs/namei.c:3807 [inline]
SYSC_mkdir fs/namei.c:3834 [inline]
SyS_mkdir+0xd4/0x2a0 fs/namei.c:3832
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x454e79
RSP: 002b:00007f4670a2fc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 00007f4670a306d4 RCX: 0000000000454e79
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000080
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000003ea R14: 00000000006f7e90 R15: 0000000000000000
Code: 00 8b b2 74 08 00 00 85 f6 0f 85 91 01 00 00 48 c7 c7 60 27 51 88 48
b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 <0f> 85 d4 03
00 00 48 83 3d 4c ab f9 06 00 0f 84 20 03 00 00 9c


---
This bug is generated by a dumb bot. It may contain errors.
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[syzbot]