Messages in this thread | | | From | Vaibhav Jain <> | Subject | Re: [PATCH] powerpc/xmon: really enable xmon when a breakpoint is set | Date | Tue, 22 May 2018 12:53:53 +0530 |
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Thanks for the patch Michal,
Michal Suchanek <msuchanek@suse.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@linux.vnet.ibm.com> Linux Technology Center, IBM India Pvt. Ltd.
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