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References: <20180304173025.19520-1-vaibhav@linux.vnet.ibm.com>
From:   Balbir Singh <bsingharora@gmail.com>
Date:   Mon, 5 Mar 2018 08:29:09 +1100
Message-ID: <CAKTCnzmdB3g0Kh67Lo7HQUp=-qRROaq_3hh8dLnDdSan3guFYw@mail.gmail.com>
Subject: Re: [PATCH v2] xmon: Setup xmon debugger hooks when first break-point
 is set
To:     Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Frederic Barrat <fbarrat@linux.vnet.ibm.com>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@lists.ozlabs.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Douglas Miller <dougmill@linux.vnet.ibm.com>
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On Mon, Mar 5, 2018 at 4:30 AM, Vaibhav Jain <vaibhav@linux.vnet.ibm.com> wrote:
> Presently sysrq key for xmon('x') is registered during kernel init
> irrespective of the value of kernel param 'xmon'. Thus xmon is enabled
> even if 'xmon=off' is passed on the kernel command line. However this
> doesn't enable the kernel debugger hooks needed for instruction or data
> breakpoints. Thus when a break-point is hit with xmon=off a kernel oops
> of the form below is reported:
>
> Oops: Exception in kernel mode, sig: 5 [#1]
> < snip >
> Trace/breakpoint trap
>
> To fix this the patch checks and enables debugger hooks when an
> instruction or data break-point is set via xmon console.
>
> Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
> ---
Reviewed-by: Balbir Singh <bsingharora@gmail.com>