From:   linux@steffen.cc
To:     "Luis Claudio R . Goncalves" <lgoncalv@redhat.com>,
        linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Steffen Dirkwinkel <s.dirkwinkel@beckhoff.com>
Subject: [PATCH v5.10-rt] kernel: fork: set wake_q_sleeper.next=NULL again in dup_task_struct
Date:   Mon, 20 Mar 2023 09:03:47 +0100
Message-Id: <20230320080347.32434-1-linux@steffen.cc>
MIME-Version: 1.0
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From: Steffen Dirkwinkel <s.dirkwinkel@beckhoff.com>

Without this we get system hangs within a couple of days.
It's also reproducible in minutes with "stress-ng --exec 20".

Example error in dmesg:
INFO: task stress-ng:163916 blocked for more than 120 seconds.
      Not tainted 5.10.168-rt83 #2
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:stress-ng       state:D stack:    0 pid:163916 ppid: 72833 flags:0x00004000
Call Trace:
 __schedule+0x2bd/0x940
 preempt_schedule_lock+0x23/0x50
 rt_spin_lock_slowlock_locked+0x117/0x2c0
 rt_spin_lock_slowlock+0x51/0x80
 rt_write_lock+0x1e/0x1c0
 do_exit+0x3ac/0xb20
 do_group_exit+0x39/0xb0
 get_signal+0x145/0x960
 ? wake_up_new_task+0x21f/0x3c0
 arch_do_signal_or_restart+0xf1/0x830
 ? __x64_sys_futex+0x146/0x1d0
 exit_to_user_mode_prepare+0x116/0x1a0
 syscall_exit_to_user_mode+0x28/0x190
 entry_SYSCALL_64_after_hwframe+0x61/0xc6
RIP: 0033:0x7f738d9074a7
RSP: 002b:00007ffdafda3cb0 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00000000000000ca RCX: 00007f738d9074a7
RDX: 0000000000028051 RSI: 0000000000000000 RDI: 00007f738be949d0
RBP: 00007ffdafda3d88 R08: 0000000000000000 R09: 00007f738be94700
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000028051
R13: 00007f738be949d0 R14: 00007ffdafda51e0 R15: 00007f738be94700

Fixes: 1ba44dcf789d ("Merge tag 'v5.10.162' into v5.10-rt")
Signed-off-by: Steffen Dirkwinkel <s.dirkwinkel@beckhoff.com>
---
 kernel/fork.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index c6e0d555fca9..0c4c20eb762c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -949,6 +949,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	tsk->splice_pipe = NULL;
 	tsk->task_frag.page = NULL;
 	tsk->wake_q.next = NULL;
+	tsk->wake_q_sleeper.next = NULL;
 	tsk->pf_io_worker = NULL;
 
 	account_kernel_stack(tsk, 1);
-- 
2.40.0