INFO: task hung in __bread_gfp

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
642e7fd23353e22290e3d51719fcb658dc252342 (Tue Apr 3 04:22:12 2018 +0000)
Merge branch 'syscalls-next' of
git://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=41f78d46e6ed1707e54a

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=4879489586692096
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-6874493495260513980
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+41f78d...@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.

binder: 20915:20965 transaction failed 29201/-71, size 0-0 line 2763
binder: 20915:20922 transaction failed 29189/-3, size 0-0 line 2963
binder: undelivered TRANSACTION_COMPLETE
binder: undelivered TRANSACTION_ERROR: 29189
binder: undelivered TRANSACTION_ERROR: 29201
INFO: task syz-executor4:20943 blocked for more than 120 seconds.
Not tainted 4.16.0+ #377
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4 D20360 20943 4546 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2848 [inline]
__schedule+0x8fb/0x1ef0 kernel/sched/core.c:3490
schedule+0xf5/0x430 kernel/sched/core.c:3549
io_schedule+0x1c/0x70 kernel/sched/core.c:5169
bit_wait_io+0x18/0x90 kernel/sched/wait_bit.c:207
__wait_on_bit+0x88/0x130 kernel/sched/wait_bit.c:48
out_of_line_wait_on_bit+0x204/0x3a0 kernel/sched/wait_bit.c:63
wait_on_bit_io include/linux/wait_bit.h:101 [inline]
__wait_on_buffer fs/buffer.c:118 [inline]
wait_on_buffer include/linux/buffer_head.h:356 [inline]
__bread_slow fs/buffer.c:1192 [inline]
__bread_gfp+0x1fc/0x2a0 fs/buffer.c:1373
__bread include/linux/buffer_head.h:398 [inline]
btrfs_read_dev_one_super+0xb1/0x270 fs/btrfs/disk-io.c:3153
btrfs_read_dev_super+0x6a/0xd0 fs/btrfs/disk-io.c:3188
btrfs_get_bdev_and_sb+0x153/0x2d0 fs/btrfs/volumes.c:386
btrfs_open_one_device fs/btrfs/volumes.c:674 [inline]
__btrfs_open_devices+0x1b6/0xc20 fs/btrfs/volumes.c:1088
btrfs_open_devices+0xa1/0xb0 fs/btrfs/volumes.c:1116
btrfs_mount_root+0x90a/0x1f40 fs/btrfs/super.c:1564
mount_fs+0x66/0x2d0 fs/super.c:1222
vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
vfs_kern_mount+0x40/0x60 fs/namespace.c:1027
btrfs_mount+0x3f9/0x1fec fs/btrfs/super.c:1657
mount_fs+0x66/0x2d0 fs/super.c:1222
vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
vfs_kern_mount fs/namespace.c:2514 [inline]
do_new_mount fs/namespace.c:2517 [inline]
do_mount+0xea4/0x2b90 fs/namespace.c:2847
ksys_mount+0xab/0x120 fs/namespace.c:3063
SYSC_mount fs/namespace.c:3077 [inline]
SyS_mount+0x39/0x50 fs/namespace.c:3074
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x457d0a
RSP: 002b:00007fed76b91bb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00000000200000c0 RCX: 0000000000457d0a
RDX: 00000000200000c0 RSI: 0000000020000100 RDI: 00007fed76b91c00
RBP: 0000000000000001 R08: 0000000020016000 R09: 00000000200000c0
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000013
R13: 0000000000000663 R14: 00000000006fc9e8 R15: 0000000000000000

Showing all locks held in the system:
2 locks held by khungtaskd/878:
#0: 000000007f318028 (rcu_read_lock){....}, at:
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: 000000007f318028 (rcu_read_lock){....}, at: watchdog+0x1d6/0xd70
kernel/hung_task.c:249
#1: 00000000e39f6bb8 (tasklist_lock){.+.+}, at:
debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
2 locks held by getty/4470:
#0: 00000000ac23a10b (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000003aa93b4 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4471:
#0: 00000000d625482b (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000641b8c03 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4472:
#0: 00000000a5f37aa9 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 0000000074a6c352 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4473:
#0: 00000000c5c23e83 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000004fc0c8e2 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4474:
#0: 00000000ee1647a5 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000184883c3 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4475:
#0: 00000000b3cd9257 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 000000006d238066 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/20363:
#0: 00000000cd3741d7 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: 00000000df77adec (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
1 lock held by syz-executor4/20943:
#0: 00000000fd97128b (uuid_mutex){+.+.}, at: btrfs_open_devices+0x27/0xb0
fs/btrfs/volumes.c:1111

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

NMI backtrace for cpu 1
CPU: 1 PID: 878 Comm: khungtaskd Not tainted 4.16.0+ #377
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+0x1a7/0x27d lib/dump_stack.c:53
nmi_cpu_backtrace+0x1e0/0x220 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
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+0x969/0xd70 kernel/hung_task.c:249
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.16.0+ #377
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:__do_softirq+0x0/0xb85
RSP: 0018:ffff8801db007cd0 EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff8801d9af8200 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffffff88ecc859
RBP: ffff8801db007ce0 R08: ffffed003b6046c3 R09: ffffed003b6046c3
R10: 0000000000000001 R11: ffffed003b6046c2 R12: ffff8801db02c480
R13: ffffffff88475200 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000021dd000 CR3: 000000000846a001 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
scheduler_ipi+0x4ab/0xa40 kernel/sched/core.c:1778
smp_reschedule_interrupt+0xe6/0x650 arch/x86/kernel/smp.c:277
reschedule_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:886
</IRQ>
RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54
RSP: 0018:ffffffff88407c38 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff02
RAX: dffffc0000000000 RBX: 1ffffffff1080f8a RCX: 0000000000000000
RDX: 1ffffffff10a2558 RSI: 0000000000000001 RDI: ffffffff88512ac0
RBP: ffffffff88407c38 R08: ffffed003b6046c3 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff88407cf0 R14: ffffffff88ecc7a0 R15: 0000000000000000
arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
default_idle+0xbf/0x430 arch/x86/kernel/process.c:354
arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:345
default_idle_call+0x36/0x90 kernel/sched/idle.c:93
cpuidle_idle_call kernel/sched/idle.c:151 [inline]
do_idle+0x24a/0x3b0 kernel/sched/idle.c:241
cpu_startup_entry+0x104/0x120 kernel/sched/idle.c:346
rest_init+0xed/0xf0 init/main.c:437
start_kernel+0x7f1/0x819 init/main.c:717
x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:443
x86_64_start_kernel+0x77/0x7a arch/x86/kernel/head64.c:424
secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:242
Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <55> 48 ba 00
00 00 00 00 fc ff df 48 89 e5 41 57 41 56 48 8d 85


---
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[syzbot]

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