• Linus Torvalds's avatar
    Fix get_user_pages() race for write access · 4ceb5db9
    Linus Torvalds authored
    There's no real guarantee that handle_mm_fault() will always be able to
    break a COW situation - if an update from another thread ends up
    modifying the page table some way, handle_mm_fault() may end up
    requiring us to re-try the operation.
    That's normally fine, but get_user_pages() ended up re-trying it as a
    read, and thus a write access could in theory end up losing the dirty
    bit or be done on a page that had not been properly COW'ed.
    This makes get_user_pages() always retry write accesses as write
    accesses by making "follow_page()" require that a writable follow has
    the dirty bit set.  That simplifies the code and solves the race: if the
    COW break fails for some reason, we'll just loop around and try again.
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
memory.c 58.5 KB