Re: [PATCH v2 1/2] livepatch/module: Apply patch when loaded module is unformed

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Fri, Mar 06, 2015 at 03:00:13PM +0100, Petr Mladek wrote:
> This brings me back to the original idea with that boolean that
> marks the state before and after the coming notifier (module_init).
> We could use a bitfield instead of the two booleans when requested.

Yeah, that would work.  Though I think one boolean is enough?

For example, just have a mod->klp_live which is initialized to false,
with its value set in the COMING notifier, and cleared in the GOING
notifier.

> Alternative solutions:
> 
> + reject new patches when a module is coming; this is ugly
> 
> + wait with adding new patch until the module leaves the COMING state;
> this might be dangerous or complicated; we would need to leave
> kgr_lock in the middle of the patch registration to avoid a deadlock
> with klp_module_init(); also we might need a waitqueue for each module
> which seems to be even bigger overhead than the two booleans
> 
> + always register/enable new patches and fix up the potential mess
> (registered patches order) in klp_module_init(); This is nasty and
> prone to regressions in the future development;
> 
> + add another MODULE_STATE where the kallsyms are visible but the
> module is not used yet; this looks to complex; the module states are
> checked on "many" locations
> 
> 
> I will wait with v3 over the weekend. I hope that it will bring fresh
> mind. Sigh, if I could have slept more with the baby twins.

Good luck!  In my experience, an entire weekend with babies is far from
restful ;-)

-- 
Josh