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Otherwise further notifier >>>> registrations using register_mt_adistance_algorithm() will find a >>>> notifier chain likely corrupted. This is the case when a CXL Type2 >>>> driver will load after kernel initialization and a CXL region created from >>>> its committed HDM decoders registers an mt_adistance_algorithm notifier. >>>> >>>> Signed-off-by: Alejandro Lucero >>>> >>>> Not sure what you mean here. The way I understand your comment leads to >>>> contradictions ... >>>> >>>> >>>> "keep unconditional removal" suggest to me unregistering hmat_adist_nb but >>>> "keep" confuses me as it is not unregister now only memory released based on >>>> __meminitdata ... but maybe you mean exactly what I did and avoid any change >>>> to __meminitdata declaration based on a config attribute, what is what Dave >>>> is suggesting to explore. >>>> >>>> >>>> Please, could you clarify this? >>>> > Sorry for the ambiguity, and yes, the last reading is what I meant. > I mean your patch's removal of the "__meminitdata", not unregistering > the notifier. > I think it would be better not to replace it with a conditional macro. > > To be more clear about what I understand, > 1. with MEMORY_HOTPLUG=n, "__meminitdata == __initdata", so hmat_adist_nb > lives in ".init.data" > 2. hmat_init() registers it, the mt_adistance_algorithms chain will hold a pointer to it, nothing ever unregister it. > 3. When boot finishes, free_initmem() discards all ".init.data". The chain still points at that freed memory. > 4. Any later register_mt_adistance_algorithm() call walks the chain and deref that stale pointer , causing use-after-free > > Note that, register_mt_adistance_algorithm() is an exported API, so any module > loaded at runtime can trigger it, not only CXL. Dropping __meminitdata > unconditionally closes the use-after-free for all caller, and the cost is just > one notifier_block staying resident. > > Hope this clarify my point. Hi Richard, Yes, this is clear now. I will send a v2 adding the Fixes tag and your point about the problem not limited to MEMORY_HOTPLUG config. Thanks!