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SubjectINFO: task hung in __x64_sys_io_uring_enter
From
Hello,

syzbot found the following crash on:

HEAD commit: bcb67f0f Add linux-next specific files for 20190412
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15c15fc3200000
kernel config: https://syzkaller.appspot.com/x/.config?x=35c479ecf64ba753
dashboard link: https://syzkaller.appspot.com/bug?extid=91ba19608804b5c53ca7
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+91ba19608804b5c53ca7@syzkaller.appspotmail.com

INFO: task syz-executor.3:27713 blocked for more than 143 seconds.
Not tainted 5.1.0-rc4-next-20190412 #24
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D29480 27713 7953 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2877 [inline]
__schedule+0x817/0x1cc0 kernel/sched/core.c:3518
schedule+0x92/0x180 kernel/sched/core.c:3562
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3620
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1310 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
__do_sys_io_uring_enter fs/io_uring.c:2697 [inline]
__se_sys_io_uring_enter fs/io_uring.c:2634 [inline]
__x64_sys_io_uring_enter+0x7de/0xac0 fs/io_uring.c:2634
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458c29
Code: cc 64 48 8b 0c 25 f8 ff ff ff 48 3b 61 10 0f 86 df 00 00 00 48 83 ec
30 48 89 6c 24 28 48 8d 6c 24 28 48 8b 42 08 48 8b 48 70 <48> 89 4c 24 20
48 8b 10 48 89 54 24 18 48 8b 40 08 48 89 44 24 10
RSP: 002b:00007f6f44f0ec78 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 0000000000458c29
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000003 R11: 0000000000000246 R12: 00007f6f44f0f6d4
R13: 00000000004bfe3c R14: 00000000004d2120 R15: 00000000ffffffff
INFO: task syz-executor.3:27724 blocked for more than 143 seconds.
Not tainted 5.1.0-rc4-next-20190412 #24
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.3 D30320 27724 7953 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2877 [inline]
__schedule+0x817/0x1cc0 kernel/sched/core.c:3518
schedule+0x92/0x180 kernel/sched/core.c:3562
schedule_timeout+0x717/0xc50 kernel/time/timer.c:1783
do_wait_for_common kernel/sched/completion.c:83 [inline]
__wait_for_common kernel/sched/completion.c:104 [inline]
wait_for_common kernel/sched/completion.c:115 [inline]
wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
__io_uring_register+0xb6/0x1fd0 fs/io_uring.c:2926
__do_sys_io_uring_register fs/io_uring.c:2976 [inline]
__se_sys_io_uring_register fs/io_uring.c:2958 [inline]
__x64_sys_io_uring_register+0x193/0x1f0 fs/io_uring.c:2958
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458c29
Code: cc 64 48 8b 0c 25 f8 ff ff ff 48 3b 61 10 0f 86 df 00 00 00 48 83 ec
30 48 89 6c 24 28 48 8d 6c 24 28 48 8b 42 08 48 8b 48 70 <48> 89 4c 24 20
48 8b 10 48 89 54 24 18 48 8b 40 08 48 89 44 24 10
RSP: 002b:00007f6f44eccc78 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000458c29
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 000000000073c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6f44ecd6d4
R13: 00000000004cb6f0 R14: 00000000004d2168 R15: 00000000ffffffff

Showing all locks held in the system:
1 lock held by khungtaskd/1041:
#0: 00000000646c174a (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:5061
2 locks held by getty/7909:
#0: 000000004ed5ef6e (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 0000000015f069f9 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/7910:
#0: 0000000028dc5235 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 000000003e5c2584 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/7911:
#0: 0000000009c1d545 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 0000000097341bd0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/7912:
#0: 00000000e304bd09 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 00000000fbaacf70 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/7913:
#0: 00000000aac8c1e7 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 00000000eb37cc5c (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/7914:
#0: 00000000dd76f9bc (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 000000003dfcb9c8 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
2 locks held by getty/7915:
#0: 00000000859ecc38 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:341
#1: 0000000086483d71 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2156
1 lock held by syz-executor.3/27713:
#0: 0000000060ca5ec1 (&ctx->uring_lock){+.+.}, at: __do_sys_io_uring_enter
fs/io_uring.c:2697 [inline]
#0: 0000000060ca5ec1 (&ctx->uring_lock){+.+.}, at: __se_sys_io_uring_enter
fs/io_uring.c:2634 [inline]
#0: 0000000060ca5ec1 (&ctx->uring_lock){+.+.}, at:
__x64_sys_io_uring_enter+0x7de/0xac0 fs/io_uring.c:2634
1 lock held by syz-executor.3/27724:
#0: 0000000060ca5ec1 (&ctx->uring_lock){+.+.}, at:
__do_sys_io_uring_register fs/io_uring.c:2975 [inline]
#0: 0000000060ca5ec1 (&ctx->uring_lock){+.+.}, at:
__se_sys_io_uring_register fs/io_uring.c:2958 [inline]
#0: 0000000060ca5ec1 (&ctx->uring_lock){+.+.}, at:
__x64_sys_io_uring_register+0x182/0x1f0 fs/io_uring.c:2958

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

NMI backtrace for cpu 1
CPU: 1 PID: 1041 Comm: khungtaskd Not tainted 5.1.0-rc4-next-20190412 #24
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:204 [inline]
watchdog+0x9b7/0xec0 kernel/hung_task.c:288
kthread+0x357/0x430 kernel/kthread.c:254
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 1 to CPUs 0:


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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