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From:   "Leonard, Niall" <Niall.Leonard@ncr.com>
To:     "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>,
        "linux@steffen.cc" <linux@steffen.cc>
CC:     "linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Steffen Dirkwinkel <s.dirkwinkel@beckhoff.com>
Subject: Re: [PATCH v5.10-rt] kernel: fork: set wake_q_sleeper.next=NULL again
 in dup_task_struct
Thread-Topic: [PATCH v5.10-rt] kernel: fork: set wake_q_sleeper.next=NULL
 again in dup_task_struct
Thread-Index: AQHZWwKU7AYdn8EL3kGBdr8btuge0K8DgwUAgASRkcE=
Date:   Thu, 23 Mar 2023 08:59:43 +0000
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References: <20230320080347.32434-1-linux@steffen.cc>
 <ZBg+3pGG9v+hQFYI@uudg.org>
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I have just checked the 5.15-rt branch on stable-rt and it is also missing =
this line.=0A=
=0A=
________________________________________=0A=
From: Luis Claudio R. Goncalves <lgoncalv@redhat.com>=0A=
Sent: 20 March 2023 11:10=0A=
To: linux@steffen.cc=0A=
Cc: linux-rt-users@vger.kernel.org; linux-kernel@vger.kernel.org; Steffen D=
irkwinkel=0A=
Subject: Re: [PATCH v5.10-rt] kernel: fork: set wake_q_sleeper.next=3DNULL =
again in dup_task_struct=0A=
=0A=
*External Message* - Use caution before opening links or attachments=0A=
=0A=
On Mon, Mar 20, 2023 at 09:03:47AM +0100, linux@steffen.cc wrote:=0A=
> From: Steffen Dirkwinkel <s.dirkwinkel@beckhoff.com>=0A=
>=0A=
> Without this we get system hangs within a couple of days.=0A=
> It's also reproducible in minutes with "stress-ng --exec 20".=0A=
>=0A=
> Example error in dmesg:=0A=
> INFO: task stress-ng:163916 blocked for more than 120 seconds.=0A=
>       Not tainted 5.10.168-rt83 #2=0A=
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.=
=0A=
> task:stress-ng       state:D stack:    0 pid:163916 ppid: 72833 flags:0x0=
0004000=0A=
> Call Trace:=0A=
>  __schedule+0x2bd/0x940=0A=
>  preempt_schedule_lock+0x23/0x50=0A=
>  rt_spin_lock_slowlock_locked+0x117/0x2c0=0A=
>  rt_spin_lock_slowlock+0x51/0x80=0A=
>  rt_write_lock+0x1e/0x1c0=0A=
>  do_exit+0x3ac/0xb20=0A=
>  do_group_exit+0x39/0xb0=0A=
>  get_signal+0x145/0x960=0A=
>  ? wake_up_new_task+0x21f/0x3c0=0A=
>  arch_do_signal_or_restart+0xf1/0x830=0A=
>  ? __x64_sys_futex+0x146/0x1d0=0A=
>  exit_to_user_mode_prepare+0x116/0x1a0=0A=
>  syscall_exit_to_user_mode+0x28/0x190=0A=
>  entry_SYSCALL_64_after_hwframe+0x61/0xc6=0A=
> RIP: 0033:0x7f738d9074a7=0A=
> RSP: 002b:00007ffdafda3cb0 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca=0A=
> RAX: fffffffffffffe00 RBX: 00000000000000ca RCX: 00007f738d9074a7=0A=
> RDX: 0000000000028051 RSI: 0000000000000000 RDI: 00007f738be949d0=0A=
> RBP: 00007ffdafda3d88 R08: 0000000000000000 R09: 00007f738be94700=0A=
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000028051=0A=
> R13: 00007f738be949d0 R14: 00007ffdafda51e0 R15: 00007f738be94700=0A=
>=0A=
> Fixes: 1ba44dcf789d ("Merge tag 'v5.10.162' into v5.10-rt")=0A=
=0A=
Thank you for spotting and investigating that!=0A=
=0A=
I dropped that specific line while fixing a small merge conflict from=0A=
=0A=
    788d0824269b io_uring: import 5.15-stable io_uring=0A=
=0A=
Interestingly enough, I didn't see that problem while running stress-ng.=0A=
I may need to add a few more, different, systems to my test base.=0A=
=0A=
Anyway, I will add this fix to the next build.=0A=
=0A=
Luis=0A=
=0A=
=0A=
> Signed-off-by: Steffen Dirkwinkel <s.dirkwinkel@beckhoff.com>=0A=
> ---=0A=
>  kernel/fork.c | 1 +=0A=
>  1 file changed, 1 insertion(+)=0A=
>=0A=
> diff --git a/kernel/fork.c b/kernel/fork.c=0A=
> index c6e0d555fca9..0c4c20eb762c 100644=0A=
> --- a/kernel/fork.c=0A=
> +++ b/kernel/fork.c=0A=
> @@ -949,6 +949,7 @@ static struct task_struct *dup_task_struct(struct tas=
k_struct *orig, int node)=0A=
>       tsk->splice_pipe =3D NULL;=0A=
>       tsk->task_frag.page =3D NULL;=0A=
>       tsk->wake_q.next =3D NULL;=0A=
> +     tsk->wake_q_sleeper.next =3D NULL;=0A=
>       tsk->pf_io_worker =3D NULL;=0A=
>=0A=
>       account_kernel_stack(tsk, 1);=0A=
> --=0A=
> 2.40.0=0A=
>=0A=
---end quoted text---=0A=
=0A=