Re: INFO: task hung in blk_freeze_queue

Re: INFO: task hung in blk_freeze_queue

[Dmitry Vyukov]

On Wed, Feb 7, 2018 at 8:46 AM, syzbot
<syzbot+2ab52b8d94df5e2eaa01@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on upstream commit
> e237f98a9c134c3d600353f21e07db915516875b (Mon Feb 5 21:35:56 2018 +0000)
> Merge tag 'xfs-4.16-merge-5' of
> git://git.kernel.org/pub/scm/fs/xfs/xfs-linux
>
> So far this crash happened 2 times on upstream.
> Unfortunately, I don't have any reproducer for this crash yet.
> Raw console output is attached.
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached.
> user-space arch: i386


Looks similar to this one:

#syz dup: INFO: task hung in lo_ioctl


> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+2ab52b8d94df5e2eaa01@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.
>
> Buffer I/O error on dev loop0, logical block 0, lost async page write
> INFO: task syz-executor1:14117 blocked for more than 120 seconds.
>       Not tainted 4.15.0+ #210
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor1   D26432 14117   4227 0x20020004
> Call Trace:
>  context_switch kernel/sched/core.c:2845 [inline]
>  __schedule+0x8eb/0x2060 kernel/sched/core.c:3421
>  schedule+0xf5/0x430 kernel/sched/core.c:3480
>  blk_mq_freeze_queue_wait+0x1bb/0x400 block/blk-mq.c:136
>  blk_freeze_queue+0x4a/0x80 block/blk-mq.c:165
>  blk_mq_freeze_queue+0x15/0x20 block/blk-mq.c:174
>  loop_change_fd drivers/block/loop.c:667 [inline]
>  lo_ioctl+0x10ce/0x1b70 drivers/block/loop.c:1361
>  lo_compat_ioctl+0xab/0x140 drivers/block/loop.c:1556
>  compat_blkdev_ioctl+0x3ae/0x1840 block/compat_ioctl.c:406
>  C_SYSC_ioctl fs/compat_ioctl.c:1473 [inline]
>  compat_SyS_ioctl+0x151/0x2a30 fs/compat_ioctl.c:1419
>  do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
>  do_fast_syscall_32+0x3ee/0xfa1 arch/x86/entry/common.c:392
>  entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
> RIP: 0023:0xf7f44c79
> RSP: 002b:00000000f774008c EFLAGS: 00000296 ORIG_RAX: 0000000000000036
> RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000000004c06
> RDX: 0000000000000013 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>
> Showing all locks held in the system:
> 2 locks held by khungtaskd/759:
>  #0:  (rcu_read_lock){....}, at: [<00000000b3b533f6>]
> check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
>  #0:  (rcu_read_lock){....}, at: [<00000000b3b533f6>] watchdog+0x1c5/0xd60
> kernel/hung_task.c:249
>  #1:  (tasklist_lock){.+.+}, at: [<00000000440cd9e2>]
> debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
> 1 lock held by rsyslogd/4029:
>  #0:  (&f->f_pos_lock){+.+.}, at: [<000000007729bd98>]
> __fdget_pos+0x12b/0x190 fs/file.c:765
> 2 locks held by getty/4151:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000903280c4>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000fb09d1cd>]
> n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4152:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000903280c4>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000fb09d1cd>]
> n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4153:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000903280c4>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000fb09d1cd>]
> n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4154:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000903280c4>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000fb09d1cd>]
> n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4155:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000903280c4>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000fb09d1cd>]
> n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4156:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000903280c4>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000fb09d1cd>]
> n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4157:
>  #0:  (&tty->ldisc_sem){++++}, at: [<00000000903280c4>]
> ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
>  #1:  (&ldata->atomic_read_lock){+.+.}, at: [<00000000fb09d1cd>]
> n_tty_read+0x2ef/0x1a00 drivers/tty/n_tty.c:2131
> 1 lock held by syz-executor1/14117:
>  #0:  (&lo->lo_ctl_mutex/1){+.+.}, at: [<00000000b6589539>]
> lo_ioctl+0x8b/0x1b70 drivers/block/loop.c:1355
>
> =============================================
>
> NMI backtrace for cpu 1
> CPU: 1 PID: 759 Comm: khungtaskd Not tainted 4.15.0+ #210
> 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+0x194/0x257 lib/dump_stack.c:53
>  nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
>  nmi_trigger_cpumask_backtrace+0x122/0x180 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+0x90c/0xd60 kernel/hung_task.c:249
>  kthread+0x33c/0x400 kernel/kthread.c:238
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:429
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10
> arch/x86/include/asm/irqflags.h:54
>
>
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
> Direct all questions to syzkaller@googlegroups.com.
>
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is
> merged
> into any tree, please reply to this email with:
> #syz fix: exact-commit-title
> To mark this as a duplicate of another syzbot report, please reply with:
> #syz dup: exact-subject-of-another-report
> If it's a one-off invalid bug report, please reply with:
> #syz invalid
> Note: if the crash happens again, it will cause creation of a new bug
> report.
> Note: all commands must start from beginning of the line in the email body.
>
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Re: INFO: task hung in blk_freeze_queue

[Tetsuo Handa]

A patch for this specific report is ready. I don't know whether other
"dup" reports will be solved by this patch. Thus, I "undup" this report.

#syz undup

>From eed54c6ae475860a9c63b37b58f34735e792eef7 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 5 May 2018 12:59:12 +0900
Subject: [PATCH] block/loop: Add recursion check for LOOP_CHANGE_FD request.

syzbot is reporting hung tasks at blk_freeze_queue() [1]. This is
due to ioctl(loop_fd, LOOP_CHANGE_FD, loop_fd) request which should be
rejected. Fix this by adding same recursion check which is used by
LOOP_SET_FD request.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+2ab52b8d94df5e2eaa01@syzkaller.appspotmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
---
 drivers/block/loop.c | 59 ++++++++++++++++++++++++++++++++--------------------
 1 file changed, 37 insertions(+), 22 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 5d4e316..cee3c01 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -644,6 +644,34 @@ static void loop_reread_partitions(struct loop_device *lo,
 			__func__, lo->lo_number, lo->lo_file_name, rc);
 }
 
+static inline int is_loop_device(struct file *file)
+{
+	struct inode *i = file->f_mapping->host;
+
+	return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR;
+}
+
+static int check_loop_recursion(struct file *f, struct block_device *bdev)
+{
+	/*
+	 * FIXME: Traversing on other loop devices without corresponding
+	 * lo_ctl_mutex is not safe. l->lo_state can become Lo_rundown and
+	 * l->lo_backing_file can become NULL when raced with LOOP_CLR_FD.
+	 */
+	while (is_loop_device(f)) {
+		struct loop_device *l;
+
+		if (f->f_mapping->host->i_bdev == bdev)
+			return -EBUSY;
+
+		l = f->f_mapping->host->i_bdev->bd_disk->private_data;
+		if (l->lo_state == Lo_unbound)
+			return -EINVAL;
+		f = l->lo_backing_file;
+	}
+	return 0;
+}
+
 /*
  * loop_change_fd switched the backing store of a loopback device to
  * a new file. This is useful for operating system installers to free up
@@ -673,6 +701,11 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 	if (!file)
 		goto out;
 
+	/* Avoid recursion */
+	error = check_loop_recursion(file, bdev);
+	if (error)
+		goto out_putf;
+
 	inode = file->f_mapping->host;
 	old_file = lo->lo_backing_file;
 
@@ -706,13 +739,6 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
 	return error;
 }
 
-static inline int is_loop_device(struct file *file)
-{
-	struct inode *i = file->f_mapping->host;
-
-	return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR;
-}
-
 /* loop sysfs attributes */
 
 static ssize_t loop_attr_show(struct device *dev, char *page,
@@ -877,7 +903,7 @@ static int loop_prepare_queue(struct loop_device *lo)
 static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 		       struct block_device *bdev, unsigned int arg)
 {
-	struct file	*file, *f;
+	struct file	*file;
 	struct inode	*inode;
 	struct address_space *mapping;
 	int		lo_flags = 0;
@@ -897,20 +923,9 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 		goto out_putf;
 
 	/* Avoid recursion */
-	f = file;
-	while (is_loop_device(f)) {
-		struct loop_device *l;
-
-		if (f->f_mapping->host->i_bdev == bdev)
-			goto out_putf;
-
-		l = f->f_mapping->host->i_bdev->bd_disk->private_data;
-		if (l->lo_state == Lo_unbound) {
-			error = -EINVAL;
-			goto out_putf;
-		}
-		f = l->lo_backing_file;
-	}
+	error = check_loop_recursion(file, bdev);
+	if (error)
+		goto out_putf;
 
 	mapping = file->f_mapping;
 	inode = mapping->host;
-- 
1.8.3.1

Re: INFO: task hung in blk_freeze_queue

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    cdface520934 Merge tag 'for_linus_stable' of git://git.ker..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136c8ee7800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=61c12b53c2a25ec4
dashboard link: https://syzkaller.appspot.com/bug?extid=2ab52b8d94df5e2eaa01
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=15afa247800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16f07717800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2ab52b8d94df5e2eaa01@syzkaller.appspotmail.com

INFO: task syz-executor148:4500 blocked for more than 120 seconds.
       Not tainted 4.17.0-rc2+ #23
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor148 D16648  4500   4481 0x00000000
Call Trace:
  context_switch kernel/sched/core.c:2848 [inline]
  __schedule+0x801/0x1e30 kernel/sched/core.c:3490
  schedule+0xef/0x430 kernel/sched/core.c:3549
  blk_mq_freeze_queue_wait+0x1ce/0x460 block/blk-mq.c:136
  blk_freeze_queue+0x4a/0x80 block/blk-mq.c:165
  blk_mq_freeze_queue+0x15/0x20 block/blk-mq.c:174
  loop_clr_fd+0x226/0xb80 drivers/block/loop.c:1047
  lo_ioctl+0x642/0x2130 drivers/block/loop.c:1404
  __blkdev_driver_ioctl block/ioctl.c:303 [inline]
  blkdev_ioctl+0x9b6/0x2020 block/ioctl.c:601
  block_ioctl+0xee/0x130 fs/block_dev.c:1877
  vfs_ioctl fs/ioctl.c:46 [inline]
  file_ioctl fs/ioctl.c:500 [inline]
  do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
  __do_sys_ioctl fs/ioctl.c:708 [inline]
  __se_sys_ioctl fs/ioctl.c:706 [inline]
  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x449789
RSP: 002b:00007f210fae5da8 EFLAGS: 00000297 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dac3c RCX: 0000000000449789
RDX: 0000000000449789 RSI: 0000000000004c01 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000297 R12: 00000000006dac38
R13: 0030656c69662f2e R14: 6f6f6c2f7665642f R15: 0000000000000007

Showing all locks held in the system:
2 locks held by khungtaskd/893:
  #0: 0000000045f40930 (rcu_read_lock){....}, at:  
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
  #0: 0000000045f40930 (rcu_read_lock){....}, at: watchdog+0x1ff/0xf60  
kernel/hung_task.c:249
  #1: 0000000081898718 (tasklist_lock){.+.+}, at:  
debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
1 lock held by rsyslogd/4362:
  #0: 000000002e322c73 (&f->f_pos_lock){+.+.}, at: __run_timers+0x16e/0xc50  
kernel/time/timer.c:1658
2 locks held by getty/4452:
  #0: 000000003abe4bd2 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 0000000035e35fb8 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4453:
  #0: 000000004e78faf9 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 0000000044d079f2 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4454:
  #0: 0000000037bf7fca (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 00000000fc65c2e0 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4455:
  #0: 00000000650b41ff (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 00000000f8a69a89 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4456:
  #0: 0000000033547e18 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 000000000c85318d (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4457:
  #0: 00000000e5cb3908 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 000000009fc1aed4 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
2 locks held by getty/4458:
  #0: 0000000055360c24 (&tty->ldisc_sem){++++}, at:  
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
  #1: 000000002bcd4fa8 (&ldata->atomic_read_lock){+.+.}, at:  
n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
1 lock held by syz-executor148/4486:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/4500:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/4514:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/4515:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/4517:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/5006:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/5008:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/5009:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/5011:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/5012:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/5014:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391
1 lock held by syz-executor148/4483:
  #0: 0000000004c28cff (&rq->lock){-.-.}, at: rq_lock  
kernel/sched/sched.h:1799 [inline]
  #0: 0000000004c28cff (&rq->lock){-.-.}, at: __schedule+0x246/0x1e30  
kernel/sched/core.c:3428
1 lock held by blkid/5016:
  #0: 00000000bf14345a (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x2130  
drivers/block/loop.c:1391

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

NMI backtrace for cpu 1
CPU: 1 PID: 893 Comm: khungtaskd Not tainted 4.17.0-rc2+ #23
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:238
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4495 Comm: syz-executor148 Not tainted 4.17.0-rc2+ #23
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:debug_lockdep_rcu_enabled.part.1+0x3b/0x60 kernel/rcu/update.c:301
RSP: 0018:ffff8801d3ccefe0 EFLAGS: 00000046
RAX: 0000000000000007 RBX: ffff8801b142c200 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 00000000ffffffff RDI: ffff8801b142ca34
RBP: ffff8801d3ccefe8 R08: ffffed003b5c46c3 R09: ffffed003b5c46c2
R10: ffffed003b5c46c2 R11: ffff8801dae23613 R12: 1ffff1003a799e26
R13: ffff8801d3ccf170 R14: 0000000000000000 R15: ffff8801b142c200
FS:  00007f210fb07700(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f16b38df9ce CR3: 00000001b19db000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  debug_lockdep_rcu_enabled+0x77/0x90 kernel/rcu/update.c:300
  trace_rcu_utilization include/trace/events/rcu.h:21 [inline]
  rcu_note_context_switch+0x554/0x710 kernel/rcu/tree.c:456
  __schedule+0x23e/0x1e30 kernel/sched/core.c:3418
  schedule+0xef/0x430 kernel/sched/core.c:3549
  freezable_schedule include/linux/freezer.h:172 [inline]
  futex_wait_queue_me+0x3e8/0x820 kernel/futex.c:2530
  futex_wait+0x450/0x9f0 kernel/futex.c:2645
  do_futex+0x336/0x27d0 kernel/futex.c:3527
  __do_sys_futex kernel/futex.c:3587 [inline]
  __se_sys_futex kernel/futex.c:3555 [inline]
  __x64_sys_futex+0x46a/0x680 kernel/futex.c:3555
  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x449789
RSP: 002b:00007f210fb06da8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00000000006dac24 RCX: 0000000000449789
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000006dac24
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac20
R13: 0030656c69662f2e R14: 6f6f6c2f7665642f R15: 0000000000000007
Code: 48 8b 1c 25 c0 ed 01 00 48 8d bb 34 08 00 00 48 89 fa 48 c1 ea 03 0f  
b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 10 <8b> 93 34 08  
00 00 31 c0 5b 5d 85 d2 0f 94 c0 c3 e8 70 ed 51 00