linux-kernel - Re: [PATCH] exit: Detect and fix irq disabled state in oops

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Message-Id: <CP6GJNNB62LY.N38DBL6D2S79@bobo>
Date:   Tue, 20 Dec 2022 17:14:05 +1000
From:   "Nicholas Piggin" <npiggin@...il.com>
To:     "Nicholas Piggin" <npiggin@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     <linux-kernel@...r.kernel.org>,
        "Michael Ellerman" <mpe@...erman.id.au>
Subject: Re: [PATCH] exit: Detect and fix irq disabled state in oops

On Tue Oct 4, 2022 at 7:44 PM AEST, Nicholas Piggin wrote:
> If a task oopses with irqs disabled, this can cause various cascading
> problems in the oops path such as sleep-from-invalid warnings, and
> potentially worse.
>
> Since commit 0258b5fd7c712 ("coredump: Limit coredumps to a single
> thread group"), the unconditional irq enable in coredump_task_exit()
> will "fix" the irq state to be enabled early in do_exit(), so currently
> this may not be triggerable, but that is coincidental and fragile.
>
> Detect and fix the irqs_disabled() condition in the oops path before
> calling do_exit(), similarly to the way in_atomic() is handled.
>
> Reported-by: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>

Hey Eric, did you have any thoughts on this?

Thanks,
Nick

> ---
>  kernel/exit.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 84021b24f79e..fa696765f694 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -738,6 +738,7 @@ void __noreturn do_exit(long code)
>  	struct task_struct *tsk = current;
>  	int group_dead;
>  
> +	WARN_ON(irqs_disabled());
>  	WARN_ON(tsk->plug);
>  
>  	kcov_task_exit(tsk);
> @@ -865,6 +866,11 @@ void __noreturn make_task_dead(int signr)
>  	if (unlikely(!tsk->pid))
>  		panic("Attempted to kill the idle task!");
>  
> +	if (unlikely(irqs_disabled())) {
> +		pr_info("note: %s[%d] exited with irqs disabled\n",
> +			current->comm, task_pid_nr(current));
> +		local_irq_enable();
> +	}
>  	if (unlikely(in_atomic())) {
>  		pr_info("note: %s[%d] exited with preempt_count %d\n",
>  			current->comm, task_pid_nr(current),
> -- 
> 2.37.2