• Linus Torvalds's avatar
    VM: skip the stack guard page lookup in get_user_pages only for mlock · a1fde08c
    Linus Torvalds authored
    The logic in __get_user_pages() used to skip the stack guard page lookup
    whenever the caller wasn't interested in seeing what the actual page
    was.  But Michel Lespinasse points out that there are cases where we
    don't care about the physical page itself (so 'pages' may be NULL), but
    do want to make sure a page is mapped into the virtual address space.
    
    So using the existence of the "pages" array as an indication of whether
    to look up the guard page or not isn't actually so great, and we really
    should just use the FOLL_MLOCK bit.  But because that bit was only set
    for the VM_LOCKED case (and not all vma's necessarily have it, even for
    mlock()), we couldn't do that originally.
    
    Fix that by moving the VM_LOCKED check deeper into the call-chain, which
    actually simplifies many things.  Now mlock() gets simpler, and we can
    also check for FOLL_MLOCK in __get_user_pages() and the code ends up
    much more straightforward.
    Reported-and-reviewed-by: default avatarMichel Lespinasse <walken@google.com>
    Cc: stable@kernel.org
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    a1fde08c
mlock.c 15.5 KB