On Fri, Jan 27, 2023 at 12:52:38AM +0000, Al Viro wrote: > On Thu, Jan 26, 2023 at 11:56:50PM +0000, David Howells wrote: > > Al says that pinning a page (ie. FOLL_PIN) could cause a deadlock if a page is > > vmspliced into a pipe with the pipe holding a pin on it because pinned pages > > are removed from all page tables. Is this actually the case? I can't see > > offhand where in mm/gup.c it does this. > > It doesn't; sorry, really confused memories of what's going on, took a while > to sort them out (FWIW, writeback is where we unmap and check if page is > pinned, while pin_user_pages running into an unmapped page will end up > with handle_mm_fault() (->fault(), actually) try to get the sucker locked > and block on that until the writeback is over). Umm... OK, I really need to reread that area. Hopefully will be done with that by tomorrow...
