Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH] powerpc/xmon: Dont register sysrq key when kernel param xmon=off | Date | Wed, 14 Feb 2018 22:40:51 +1100 |
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Vaibhav Jain <vaibhav@linux.vnet.ibm.com> writes:
> Thanks for reviewing this patch Balbir > > Balbir Singh <bsingharora@gmail.com> writes: > >> Any specific issue you've run into without this patch? > Without this patch since xmon is still accessible via sysrq and there is > no indication/warning on the xmon console mentioning that its is not > fully functional. Specifically xmon-console would still allow user to > set instruction/data breakpoint eventhough they wont work and will > result in a kernel-oops. > > Below is command log illustrating this problem on one of my test system > where I tried setting an instruction breakpoint on cmdline_proc_show() > with xmon=off:
<snip>
But the same crash happens with XMON_DEFAULT=n and nothing on the command line.
The problem is not xmon=off on the command line.
The problem is that when xmon_on = false and we enter xmon via sysrq and then set breakpoints, we need to enable xmon_on before leaving xmon.
So this is a bug introduced by:
3b5bf42b81d5 ("powerpc/xmon: Fix an unexpected xmon on/off state change")
How to fix it is not entirely clear. In general I like the behaviour we have since the above commit, ie. quickly dropping into xmon and inspecting something doesn't leave xmon enabled, which then causes the system not to kdump/reboot later.
What would be nice is if we keep that behaviour, but any action you take in xmon that requires xmon to remain resident, ie. setting a breakpoint, calls a function which makes sure xmon_on = true and if it wasn't prints a nice message saying "Turning xmon on due to breakpoint insertion" or something.
cheers
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