linux-kernel - Re: [PATCH] panic: Ensure preemption is disabled during panic()

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Date:   Thu, 3 Oct 2019 21:53:04 +0100
From:   Will Deacon <will@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        contact@...ium.me, Russell King <linux@...linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>, stable@...r.kernel.org
Subject: Re: [PATCH] panic: Ensure preemption is disabled during panic()

Hi Andrew,

Thanks for having a look.

On Wed, Oct 02, 2019 at 02:45:58PM -0700, Andrew Morton wrote:
> On Wed,  2 Oct 2019 13:35:38 +0100 Will Deacon <will@...nel.org> wrote:
> > Disable preemption in 'panic()' before re-enabling interrupts.
> > 
> > ...
> >
> > --- a/kernel/panic.c
> > +++ b/kernel/panic.c
> > @@ -180,6 +180,7 @@ void panic(const char *fmt, ...)
> >  	 * after setting panic_cpu) from invoking panic() again.
> >  	 */
> >  	local_irq_disable();
> > +	preempt_disable_notrace();
> >  
> >  	/*
> >  	 * It's possible to come here directly from a panic-assertion and
> 
> We still do a lot of stuff (kexec, kgdb, etc) after this
> preempt_disable() and I worry that something in there will now trigger
> a might_sleep() warning as a result?

Given that interrupts are already disabled at this point, I don't think
we'll get any additional warnings here by disabling preemption as well.

Will