Re: [syzbot] [crypto?] INFO: task hung in hwrng_fillfn

From: syzbot <syzbot+c52ab18308964d248092@syzkaller.appspotmail.com>
To: eadavis@qq.com, linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [crypto?] INFO: task hung in hwrng_fillfn
Date: Tue, 28 Nov 2023 19:23:10 -0800	[thread overview]
Message-ID: <000000000000f5d076060b420d1f@google.com> (raw)
In-Reply-To: <tencent_DB6F26C7B37BA362296123A96443F7759705@qq.com>

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in hwrng_fillfn

INFO: task hwrng:729 blocked for more than 143 seconds.
      Not tainted 6.4.0-syzkaller-01647-g6e2332e0ab53-dirty #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:hwrng           state:D stack:29760 pid:729   ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0xeda/0x5b60 kernel/sched/core.c:6710
 schedule+0xe7/0x1b0 kernel/sched/core.c:6786
 schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6845
 __mutex_lock_common kernel/locking/mutex.c:679 [inline]
 __mutex_lock+0x5b4/0x990 kernel/locking/mutex.c:747
 hwrng_fillfn+0x145/0x430 drivers/char/hw_random/core.c:505
 kthread+0x2c4/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
 </TASK>

Showing all locks held in the system:
1 lock held by rcu_tasks_kthre/13:
 #0: ffffffff8c9996f0 (rcu_tasks.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x2c/0xe30 kernel/rcu/tasks.h:522
1 lock held by rcu_tasks_trace/14:
 #0: ffffffff8c9993f0 (rcu_tasks_trace.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x2c/0xe30 kernel/rcu/tasks.h:522
1 lock held by khungtaskd/28:
 #0: ffffffff8c99a300 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x340 kernel/locking/lockdep.c:6615
1 lock held by hwrng/729:
 #0: ffffffff8d4887a8 (reading_mutex){+.+.}-{3:3}, at: hwrng_fillfn+0x145/0x430 drivers/char/hw_random/core.c:505
2 locks held by getty/4749:
 #0: ffff8880287f3098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
 #1: ffffc900015b02f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xfc5/0x1460 drivers/tty/n_tty.c:2176
1 lock held by syz-executor.0/5449:
2 locks held by syz-executor.0/5450:
1 lock held by syz-executor.0/5744:
1 lock held by syz-executor.0/5762:

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

NMI backtrace for cpu 1
CPU: 1 PID: 28 Comm: khungtaskd Not tainted 6.4.0-syzkaller-01647-g6e2332e0ab53-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/10/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x277/0x390 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x2ac/0x310 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
 watchdog+0xf29/0x11b0 kernel/hung_task.c:379
 kthread+0x2c4/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5744 Comm: syz-executor.0 Not tainted 6.4.0-syzkaller-01647-g6e2332e0ab53-dirty #0

Tested on:

commit:         6e2332e0 Merge tag 'cgroup-for-6.5' of git://git.kerne..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1271b7ece80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=102b18358d5797d8
dashboard link: https://syzkaller.appspot.com/bug?extid=c52ab18308964d248092
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=147cc8b4e80000