INFO: task hung in blkdev_issue_flush (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 6fbc7275 Linux 5.2-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1218ee83a00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f6451f0da3d42d53
dashboard link: https://syzkaller.appspot.com/bug?extid=e7624af9c1ef3b617512
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13105d6da00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=120c261ba00000

The bug was bisected to:

commit a32e236eb93e62a0f692e79b7c3c9636689559b9
Author: Linus Torvalds <torv...@linux-foundation.org>
Date: Fri Aug 3 19:22:09 2018 +0000

Partially revert "block: fail op_is_write() requests to read-only
partitions"

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10fc732ba00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=12fc732ba00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14fc732ba00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e7624a...@syzkaller.appspotmail.com
Fixes: a32e236eb93e ("Partially revert "block: fail op_is_write() requests
to read-only partitions"")

INFO: task syz-executor485:8568 blocked for more than 143 seconds.
Not tainted 5.2.0-rc7 #46
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor485 D28528 8568 8564 0x00004004
Call Trace:
context_switch kernel/sched/core.c:2818 [inline]
__schedule+0x7cb/0x1560 kernel/sched/core.c:3445
schedule+0xa8/0x260 kernel/sched/core.c:3509
schedule_timeout+0x717/0xc50 kernel/time/timer.c:1783
io_schedule_timeout+0x26/0x80 kernel/sched/core.c:5119
do_wait_for_common kernel/sched/completion.c:83 [inline]
__wait_for_common kernel/sched/completion.c:104 [inline]
wait_for_common_io kernel/sched/completion.c:121 [inline]
wait_for_completion_io+0x29c/0x440 kernel/sched/completion.c:169
submit_bio_wait+0x11d/0x1c0 block/bio.c:1003
blkdev_issue_flush+0x20d/0x300 block/blk-flush.c:449
blkdev_fsync+0x95/0xd0 fs/block_dev.c:687
vfs_fsync_range+0x141/0x230 fs/sync.c:197
vfs_fsync fs/sync.c:211 [inline]
do_fsync+0x54/0xa0 fs/sync.c:221
__do_sys_fdatasync fs/sync.c:234 [inline]
__se_sys_fdatasync fs/sync.c:232 [inline]
__x64_sys_fdatasync+0x36/0x50 fs/sync.c:232
do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x449749
Code: Bad RIP value.
RSP: 002b:00007fa817de2ce8 EFLAGS: 00000246 ORIG_RAX: 000000000000004b
RAX: ffffffffffffffda RBX: 00000000006dac58 RCX: 0000000000449749
RDX: 0000000000449749 RSI: 0000000000000000 RDI: 0000000000000009
RBP: 00000000006dac50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac5c
R13: 00007fff567b6b5f R14: 00007fa817de39c0 R15: 20c49ba5e353f7cf

Showing all locks held in the system:
1 lock held by khungtaskd/1043:
#0: 00000000f7c610b3 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:5149
2 locks held by rsyslogd/8451:
#0: 00000000dfc1566f (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:801
#1: 0000000054220207 (&rq->lock){-.-.}, at: rq_lock
kernel/sched/sched.h:1168 [inline]
#1: 0000000054220207 (&rq->lock){-.-.}, at: __schedule+0x1f5/0x1560
kernel/sched/core.c:3397
2 locks held by getty/8541:
#0: 000000004ff543bd (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 000000002a3905f3 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/8542:
#0: 000000006e67fcec (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 00000000ee71e4f3 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/8543:
#0: 00000000bd0907a0 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 000000000876abce (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/8544:
#0: 00000000710d6f7d (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 00000000af289586 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/8545:
#0: 000000003399e62d (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 00000000ee97f91a (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/8546:
#0: 00000000ff2274c6 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 00000000b96c5a9f (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/8547:
#0: 000000005165f028 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 00000000e89d5b4a (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156

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

NMI backtrace for cpu 1
CPU: 1 PID: 1043 Comm: khungtaskd Not tainted 5.2.0-rc7 #46
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+0x172/0x1f0 lib/dump_stack.c:113
nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1be/0x236 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:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0x9b7/0xec0 kernel/hung_task.c:289
kthread+0x354/0x420 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0xe/0x10
arch/x86/include/asm/irqflags.h:60


---
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#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Bart Van Assche]

Since the tty layer does not call any block layer code, does this mean
that the root cause is in the tty code instead of in the block layer?

Bart.

[Eric Biggers]

#syz fix: nbd: replace kill_bdev() with __invalidate_device() again