On Wed 27-06-18 09:34:20, Michal Hocko wrote: > On Tue 26-06-18 10:04:16, Andrew Morton wrote: [...] > > Really, the changelog isn't right. There *is* a real reason to blow > > up. Effectively the caller is attempting to obtain the virtual address > > of a highmem page without having kmapped it first. That's an outright > > bug. > > And as I've argued before the code would be wrong regardless. We would > leak the memory or worse touch somebody's else kmap without knowing > that. So we have a choice between a mem leak, data corruption k or a > silent fixup. I would prefer the last option. And blowing up on a BUG > is not much better on something that is easily fixable. I am not really > convinced that & ~__GFP_HIGHMEM is something to lose sleep over. It's been some time since I've checked that changelog and you are right it should contain all the above so the changelog should be: " There is no real reason to blow up just because the caller doesn't know that __get_free_pages cannot return highmem pages. Simply fix that up silently. Even if we have some confused users such a fixup will not be harmful. On the other hand an incorrect usage can lead to either a memory leak or worse a memory corruption when the allocated page hashes to an already kmaped page. Most workloads run with CONFIG_DEBUG_VM disabled so the assert wouldn't help. " -- Michal Hocko SUSE Labs
