Messages in this thread | | | Date | Tue, 16 Aug 2022 18:15:33 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH V3] mm: fix use-after free of page_ext after race with memory-offline |
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On Tue 16-08-22 15:04:01, Charan Teja Kalla wrote: [...] > >> @@ -183,19 +184,26 @@ static inline void __set_page_owner_handle(struct page_ext *page_ext, > >> noinline void __set_page_owner(struct page *page, unsigned short order, > >> gfp_t gfp_mask) > >> { > >> - struct page_ext *page_ext = lookup_page_ext(page); > >> + struct page_ext *page_ext = page_ext_get(page); > >> depot_stack_handle_t handle; > >> > >> if (unlikely(!page_ext)) > >> return; > > Either add a comment like this > > /* save_stack can sleep in general so we have to page_ext_put */ > > > Vlastimil suggested to go for save stack first since !page_ext is mostly > unlikely. Snip from his comments: > Why not simply do the save_stack() first and then page_ext_get() just > once? It should be really rare that it's NULL, so I don't think we save > much by avoiding an unnecessary save_stack(), while the overhead of > doing two get/put instead of one will affect every call.
right see below > > https://lore.kernel.org/all/f5fd4942-b03e-1d1c-213b-9cd5283ced91@suse.cz/ > >> + page_ext_put(); > >> > >> handle = save_stack(gfp_mask); > > or just drop the initial page_ext_get altogether. This function is > > called only when page_ext is supposed to be initialized and !page_ext > > case above should be very unlikely. Or is there any reason to keep this?
^^^^^ -- Michal Hocko SUSE Labs
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