On Thu, May 31, 2018 at 02:12:00PM +0000, Christopher Lameter wrote: > On Thu, 31 May 2018, Matthew Wilcox wrote: > > > 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. > > Freeing a page in the page allocator also was traditionally not sleeping. > That has changed? No. "Your bug" being "The bug in your static analysis tool". It probably isn't following the data flow correctly (or deeply enough).
