On Thu, May 31, 2018 at 09:10:07PM +0800, Jia-Ju Bai wrote: > I write a static analysis tool (DSAC), and it finds that kfree() can sleep. > > Here is the call path for kfree(). > Please look at it *from the bottom up*. > > [FUNC] alloc_pages(GFP_KERNEL) > arch/x86/mm/pageattr.c, 756: alloc_pages in split_large_page > arch/x86/mm/pageattr.c, 1283: split_large_page in __change_page_attr Here's your bug. Coming from kfree(), we can't end up in the split_large_page() path. __change_page_attr may be called in several different circumstances in which it would have to split a large page, but the path from kfree() is not one of them. I think the path from kfree() will lead to the 'level == PG_LEVEL_4K' path, but I'm not really familiar with this x86 code. > arch/x86/mm/pageattr.c, 1391: __change_page_attr in > __change_page_attr_set_clr > arch/x86/mm/pageattr.c, 2014: __change_page_attr_set_clr in __set_pages_np > arch/x86/mm/pageattr.c, 2034: __set_pages_np in __kernel_map_pages > ./include/linux/mm.h, 2488: __kernel_map_pages in kernel_map_pages > mm/page_alloc.c, 1074: kernel_map_pages in free_pages_prepare > mm/page_alloc.c, 1264: free_pages_prepare in __free_pages_ok > mm/page_alloc.c, 4312: __free_pages_ok in __free_pages > mm/slub.c, 3914: __free_pages in kfree > > I always have an impression that kfree() never sleeps, so I feel confused > here. > So could someone please help me to find the mistake? > Thanks in advance :) > > Best wishes, > Jia-Ju Bai
