linux-kernel - Re: [PATCH v2] xmon: Setup xmon debugger hooks when first break-point is set

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Message-ID: <CAKTCnzmdB3g0Kh67Lo7HQUp=-qRROaq_3hh8dLnDdSan3guFYw@mail.gmail.com>
Date:   Mon, 5 Mar 2018 08:29:09 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Frederic Barrat <fbarrat@...ux.vnet.ibm.com>,
        "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" 
        <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Douglas Miller <dougmill@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] xmon: Setup xmon debugger hooks when first break-point
 is set

On Mon, Mar 5, 2018 at 4:30 AM, Vaibhav Jain <vaibhav@...ux.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@...ux.vnet.ibm.com>
> ---
Reviewed-by: Balbir Singh <bsingharora@...il.com>