On Mon, Dec 08, 2014 at 10:57:31AM -0800, Linus Torvalds wrote: > actually, no we cannot. Thinking some more about it, that > "get_page(page)" is wrong in _all_ cases. It actually works better for > vmalloc pages than for normal 1:1 pages, since it's actually seriously > and *horrendously* wrong for the case of random kernel addresses which > may not even be refcounted to begin with. > > So the whole "get_page()" thing is broken. Iterating over pages in a > KVEC is simply wrong, wrong, wrong. It needs to fail. > > Iterating over a KVEC to *copy* data is ok. But no page lookup stuff > or page reference things. Hmm... FWIW, for ITER_KVEC the underlying data would bloody better not go away anyway - vmalloc space or not. Protecting the object from being freed under us is caller's responsibility and caller can guarantee that. Would a variant that does kmap_to_page()/vmalloc_to_page() _without_ get_page() for ITER_KVEC work sanely? Of course, that would have to be used with matching primitive for releasing those suckers - page_cache_release() for ITER_IOVEC (and ITER_BVEC, while we are at it - those are backed with normal pages) and nothing for ITER_KVEC ones. It would make life much more pleasant for fuse and zerocopy side of 9p - the latter does pretty much that kind of thing anyway... Comments? Al, digging himself from under a huge pile of mail... -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
