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Subject: Re: [PATCH] powerpc/traps: restore recoverability of machine_check
 interrupts
From:   Christophe LEROY <christophe.leroy@c-s.fr>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, npiggin@gmail.com
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
References: <f79824d5da910441ede885fa32a25083c4cc9359.1539422122.git.christophe.leroy@c-s.fr>
Message-ID: <ab520cc1-11b7-ddc6-2393-8f1315db4db3@c-s.fr>
Date:   Mon, 15 Oct 2018 09:40:50 +0200
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Cc: stable@vger.kernel.org <stable@vger.kernel.org>

Le 13/10/2018 à 11:16, Christophe Leroy a écrit :
> commit b96672dd840f ("powerpc: Machine check interrupt is a non-
> maskable interrupt") added a call to nmi_enter() at the beginning of
> machine check restart exception handler. Due to that, in_interrupt()
> always returns true regardless of the state before entering the
> exception, and die() panics even when the system was not already in
> interrupt.
> 
> This patch calls nmi_exit() before calling die() in order to restore
> the interrupt state we had before calling nmi_enter()
> 
> Fixes: b96672dd840f ("powerpc: Machine check interrupt is a non-maskable interrupt")
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>   arch/powerpc/kernel/traps.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index fd58749b4d6b..4f880c2a6e4c 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -765,12 +765,17 @@ void machine_check_exception(struct pt_regs *regs)
>   	if (check_io_access(regs))
>   		goto bail;
>   
> -	die("Machine check", regs, SIGBUS);
> -
>   	/* Must die if the interrupt is not recoverable */
>   	if (!(regs->msr & MSR_RI))
>   		nmi_panic(regs, "Unrecoverable Machine check");
>   
> +	if (!nested)
> +		nmi_exit();
> +
> +	die("Machine check", regs, SIGBUS);
> +
> +	return;
> +
>   bail:
>   	if (!nested)
>   		nmi_exit();
>