Re: TAKE - fix O_DIRECT and uninitialized user memory

[Andrew Morton <akpm@xxxxxxxxx>]

Steve Lord <lord@xxxxxxx> wrote:
>
>       - In pagebuf_lookup, create a pagebuf which is lockable so we
>         do not lock the pages within it during I/O. Only O_DIRECT
>         does I/O on this type of pagebuf.

oops.

What happens if an application passes multiple presentations of
the same page into a single non-O_DIRECT write() or read()?

ie:

        mmap(buf, 4096, PROT_READ, MAP_FIXED, fd1, 0);
        mmap(buf+4096, 4096, PROT_READ, MAP_FIXED, fd1, 0);
        write(fd2, buf, 8192);

?