On Sat, 26 Dec 2020, Hugh Dickins wrote: > On Sun, 27 Dec 2020, Kirill A. Shutemov wrote: > > > > Here's the fixup I have so far. It doesn't blow up immediately, but please > > take a closer look. Who knows what stupid mistake I did this time. :/ > > It's been running fine on x86_64 for a couple of hours (but of course > my testing is deficient, in not detecting the case Linus spotted). > > But I just thought I'd try it on i386 (hadn't tried previous versions) > and this has a new disappointment: crashes when booting, in the "check > if the page fault is solved" in do_fault_around(). I imagine a highmem > issue with kmap of the pte address, but I'm reporting now before looking > into it further (but verified that current linux.git i386 boots up fine). This patch (like its antecedents) moves the pte_unmap_unlock() from after do_fault_around()'s "check if the page fault is solved" into filemap_map_pages() itself (which apparently does not NULLify vmf->pte after unmapping it, which is poor, but good for revealing this issue). That looks cleaner, but of course there was a very good reason for its original positioning. Maybe you want to change the ->map_pages prototype, to pass down the requested address too, so that it can report whether the requested address was resolved or not. Or it could be left to __do_fault(), or even to a repeated fault; but those would be less efficient. > > Maybe easily fixed: but does suggest this needs exposure in linux-next. > > Hugh
