linux-kernel - Re: [PATCH] pid: Add a judgment for ns null in pid_nr

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Message-ID: <20250802022550.GT222315@ZenIV>
Date: Sat, 2 Aug 2025 03:25:50 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Xiang Gao <gxxa03070307@...il.com>
Cc: brauner@...nel.org, oleg@...hat.com, mjguzik@...il.com,
	Liam.Howlett@...cle.com, joel.granados@...nel.org,
	lorenzo.stoakes@...cle.com, linux-kernel@...r.kernel.org,
	gaoxiang17 <gaoxiang17@...omi.com>
Subject: Re: [PATCH] pid: Add a judgment for ns null in pid_nr_ns

On Sat, Aug 02, 2025 at 10:21:23AM +0800, Xiang Gao wrote:
> From: gaoxiang17 <gaoxiang17@...omi.com>
> 
> __task_pid_nr_ns
>         ns = task_active_pid_ns(current);
>         pid_nr_ns(rcu_dereference(*task_pid_ptr(task, type)), ns);
>                 if (pid && ns->level <= pid->level) {
> 
> Sometimes null is returned for task_active_pid_ns. Then it will trigger kernel panic in pid_nr_ns.

In which conditions does that happen?

> 	__task_pid_nr_ns+0x74/0xd0
> 	...
> 	__handle_irq_event_percpu+0xd4/0x284
> 	handle_irq_event+0x48/0xb0

	Huh?  Just what is it doing inside an IRQ handler?
Hell, the notion of current process is not usable in those,
let alone any properties of such...

	Details, please.