On 14/02/2017 09:37, Michael Ellerman wrote: > "Guilherme G. Piccoli" <gpicc...@linux.vnet.ibm.com> writes: > >> Currently the xmon debugger is set only via kernel boot command-line. >> It's disabled by default, and can be enabled with "xmon=on" on the >> command-line. Also, xmon may be accessed via sysrq mechanism, but once >> we enter xmon via sysrq, it's kept enabled until system is rebooted, >> even if we exit the debugger. A kernel crash will then lead to xmon >> instance, instead of triggering a kdump procedure (if configured), for >> example. >> >> This patch introduces a debugfs entry for xmon, allowing user to query >> its current state and change it if desired. Basically, the "xmon" file >> to read from/write to is under the debugfs mount point, on powerpc >> directory. Reading this file will provide the current state of the >> debugger, one of the following: "on", "off", "early" or "nobt". Writing >> one of these states to the file will take immediate effect on the debugger. > > I like this in general. > > But I think we can simplify it a bit. > > I don't think we need the nobt state anymore. As far as I can see it was > added as a way to reinstate the old behaviour when the auto backtrace > mode was added, but I've never heard of anyone using it. > > If anyone hits a crash where they really need that feature they can > always just hack the code to disable the backtrace. > > So I think step 1 is a patch to drop the xmon_no_auto_backtrace stuff. > > Also I'm not sure EARLY needs to be a separate state. It's just a > one-off invocation at boot, all we really need is just a single bit of > state communicated from early_parse_xmon() to xmon_setup(), ie. a static > bool would do. > > If we agree with that, then there's only two states left, on and off, in > which case it can probably just be an int - and we can use a simple > attribute file rather than custom parsing. >
Thanks for the good suggestions Michael, I'll change the code and submit a new version. >> * I had this patch partially done for some time, and after a discussion >> at the kernel slack channel latest week, I decided to rebase and fix >> some remaining bugs. I'd change 'x' option to always disable the debugger, > > Not quite. > > 'x' should exit and leave xmon in whatever state it was previously in. Agreed! Thanks, Guilherme > > cheers >
