On 9/5/22 04:55, Feng Tang wrote: > On Sun, Sep 04, 2022 at 06:58:49PM +0800, Hyeonggon Yoo wrote: >> On Sun, Sep 04, 2022 at 05:42:33PM +0800, Feng Tang wrote: >> > On Sun, Sep 04, 2022 at 05:03:34PM +0800, Hyeonggon Yoo wrote: >> > [...] >> > > > > >> > > > > This patch is okay but with patch 4, init_object() initializes redzone/poison area >> > > > > using s->object_size, and init_kmalloc_object() fixes redzone/poison area using orig_size. >> > > > > Why not do it in init_object() in the first time? >> > > > > >> > > > > Also, updating redzone/poison area after alloc_single_from_new_slab() >> > > > > (outside list_lock, after adding slab to list) will introduce races with validation. >> > > > > >> > > > > So I think doing set_orig_size()/init_kmalloc_object() in alloc_debug_processing() would make more sense. >> > > > >> > > > Yes, this makes sense, and in v3, kmalloc redzone/poison setup was >> > > > done in alloc_debug_processing() (through init_object()). When >> > > > rebasing to v4, I met the classical problem: how to pass 'orig_size' >> > > > parameter :) >> > > > >> > > > In latest 'for-next' branch, one call path for alloc_debug_processing() >> > > > is >> > > > ___slab_alloc >> > > > get_partial >> > > > get_any_partial >> > > > get_partial_node >> > > > alloc_debug_processing >> > > > >> > > > Adding 'orig_size' paramter to all these function looks horrible, and >> > > > I couldn't figure out a good way and chosed to put those ops after >> > > > 'set_track()' >> > > >> > > IMO adding a parameter to them isn't too horrible... >> > > I don't see better solution than adding a parameter with current implementation. >> > > (Yeah, the code is quite complicated...) >> > > >> > > It won't affect performance to meaningful degree as most of >> > > allocations will be served from cpu slab or percpu partial list. >> > >> > Thanks for the suggestion! I'm fine with it and just afraid other >> > developers may dislike the extra parameter. >> > >> > The race condition you mentioned is a valid concern, and I have thought >> > about it, one way is moving the set_orig_size() after the redzone/poision >> > setup, and in 'check_object()' we can detect whether the 'orig_size' is >> > set, and skip that check if it's not set yet. As the manual validate_slab >> > triggered from sysfs interface is a rare debug activity, I think skipping >> > one object shouldn't hurt much. >> >> That will require smp_wmb()/smp_rmb() pair to make sure that >> effects of set_orig_size() to be visible after redzone/poison setup. > > Yes, synchronization is needed here. > >> Isn't it simpler to add a parameter? > > OK, I can go this way in v5 if other developers are fine. thanks How about get_partial() instantiates an on-stack structure that contains gfpflags, ret_slab, orig_size and passes pointer to that to all the nested functions. Would be similar to "struct alloc_context" in page allocation. Something like "struct partial_context pc"? > - Feng
