On Wed 2021-12-15 07:20:04, David Vernet wrote: > Petr Mladek <pmladek@xxxxxxxx> wrote on Wed [2021-Dec-15 11:06:15 +0100]: > > Well, I still believe that this is just a cargo cult. And I would prefer > > to finish the discussion about it, first, see > > https://lore.kernel.org/all/YbmlL0ZyfSuek9OB@alley/ > > No problem, I won't send out v3 until we've finished the discussion and > have consensus. I'll assume that the discussion on whether or not there is > a leak will continue on the thread you linked to above, so I won't comment > on it here. > > > Note that klp_init_*_early() functions iterate through the arrays > > using klp_for_each_*_static. While klp_free_*() functions iterate > > via the lists using klp_for_each_*_safe(). > > Correct, as I've understood it, klp_for_each_*_safe() should only iterate > over the objects that have been added to the patch and klp_object's lists, > and thus for which kobject_init() has been invoked. So if we fail a check > on 'struct klp_object' N, then we'll only iterate over the first N - 1 > objects in klp_for_each_*_safe(). > > > We should not need the pre-early-init check when the lists include only > > structures with initialized kobjects. > > Not sure I quite follow. We have to do NULL checks for obj->funcs at some > point, and per Josh's suggestion it seems cleaner to do it outside the > critical section, and before we actually invoke kobject_init(). Apologies > if I've misunderstood your point. The original purpose of klp_init_*_early() was to allow calling klp_free_patch_*() when klp_init_*() fails. The idea was to initialize all fields properly so that free functions would do the right thing. Josh's proposal adds pre-early-init() to allow calling klp_free_patch_*() already when klp_init_*_early() fails. The purpose is to make sure that klp_init_*_early() will actually never fail. This might make things somehow complicated. Any future change in klp_init_*_early() might require change in pre-early-init() to catch eventual problems earlier. Also I am not sure what to do with the existing checks in klp_init_patch_early(). I am uneasy with removing them and hoping that pre-early-init() did the right job. But if we keep the checks then klp_init_patch_early() then it might fail and the code will not be ready for this. My proposal is to use simple trick. klp_free_patch_*() iterate using the dynamic list (list_for_each_entry) while klp_init_*_early() iterate using the arrays. Now, we just need to make sure that klp_init_*_early() will only add fully initialized structures into the dynamic list. As a result, klp_free_patch() will see only the fully initialized structures and could release them. It will not see that not-yet-initialized structures but it is fine. They are not initialized and they do not need to be freed. In fact, I think that klp_init_*_early() functions already do the right thing. IMHO, if you move the module_get() then you could safely do: int klp_enable_patch(struct klp_patch *patch) { [...] if (!try_module_get(patch->mod)) { mutex_unlock(&klp_mutex); return -ENODEV; } ret = klp_init_patch_early(patch); if (ret) goto err; Note that it would need to get tested. Anyway, does it make sense now? Best Regards, Petr
