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Message-Id: <87bmd8xieu.fsf@vajain21.in.ibm.com>
Date: Tue, 22 May 2018 12:53:53 +0530
From: Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>
To: Michal Suchanek <msuchanek@...e.de>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
Balbir Singh <bsingharora@...il.com>,
Nicholas Piggin <npiggin@...il.com>,
Breno Leitao <leitao@...ian.org>,
"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
"Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>,
linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc: Michal Suchanek <msuchanek@...e.de>
Subject: Re: [PATCH] powerpc/xmon: really enable xmon when a breakpoint is set
Thanks for the patch Michal,
Michal Suchanek <msuchanek@...e.de> writes:
> When single-stepping kernel code from xmon without a debug hook enabled
> the kernel crashes. This can happen when kernel starts with xmon on
> crash disabled but xmon is entered using sysrq.
>
> Commit e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first
> break-point is set") adds force_enable_xmon function that prints
> "xmon: Enabling debugger hooks" but does not enable them.
Debugger hooks are enabled just befores debugger() is entered from
sysrq_handle_xmon(). Thats why force_enable_xmon() simply sets sets
'xmon_on=1' and exits.
The problem you are seeing is probably due to sysrq_handle_xmon()
clearing the debugger hooks on return from debugger() as xmon_on was
never set for the 's' xmon command.
> Add the call to xmon_init to install the debugger hooks in
> force_enable_xmon and also call force_enable_xmon when single-stepping
> in xmon.
Only calling force_enable_xmon() from do_step() should be suffice as on exit
from the debugger() the value of xmon_on is checked and if required the
debugger hooks are kept instead of getting cleared.
> arch/powerpc/xmon/xmon.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index a0842f1ff72c..504bd1c3d8b0 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -1275,6 +1279,7 @@ static inline void force_enable_xmon(void)
> if (!xmon_on) {
> printf("xmon: Enabling debugger hooks\n");
> xmon_on = 1;
> + xmon_init(1);
> }
> }
As mentioned above call to force_enable_xmon() is usually done in context of
sysrq_handle_xmon() which sets the debugger hooks as soon as its
entered. So I think that this hunk is not really needed.
--
Vaibhav Jain <vaibhav@...ux.vnet.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.
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