Commit 64801d19 authored by John Hubbard's avatar John Hubbard Committed by Linus Torvalds

mm/gup_benchmark: fix MAP_HUGETLB case

The MAP_HUGETLB ("-H" option) of gup_benchmark fails:

  $ sudo ./gup_benchmark -H
  mmap: Invalid argument

This is because gup_benchmark.c is passing in a file descriptor to
mmap(), but the fd came from opening up the /dev/zero file.  This
confuses the mmap syscall implementation, which thinks that, if the
caller did not specify MAP_ANONYMOUS, then the file must be a huge page
file.  So it attempts to verify that the file really is a huge page
file, as you can see here:

ksys_mmap_pgoff()
{
    if (!(flags & MAP_ANONYMOUS)) {
        retval = -EINVAL;
        if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file)))
            goto out_fput; /* THIS IS WHERE WE END UP */

    else if (flags & MAP_HUGETLB) {
        ...proceed normally, /dev/zero is ok here...

...and of course is_file_hugepages() returns "false" for the /dev/zero
file.

The problem is that the user space program, gup_benchmark.c, really just
wants anonymous memory here.  The simplest way to get that is to pass
MAP_ANONYMOUS whenever MAP_HUGETLB is specified, so that's what this
patch does.

Link: http://lkml.kernel.org/r/20191021212435.398153-2-jhubbard@nvidia.comSigned-off-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarJérôme Glisse <jglisse@redhat.com>
Cc: Keith Busch <keith.busch@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7961eee3
...@@ -71,7 +71,7 @@ int main(int argc, char **argv) ...@@ -71,7 +71,7 @@ int main(int argc, char **argv)
flags |= MAP_SHARED; flags |= MAP_SHARED;
break; break;
case 'H': case 'H':
flags |= MAP_HUGETLB; flags |= (MAP_HUGETLB | MAP_ANONYMOUS);
break; break;
default: default:
return -1; return -1;
......
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