[PATCH 5.3 073/135] mm/gup_benchmark: fix MAP_HUGETLB case

Greg Kroah-Hartman
2019-12-03T23:10:41Z

From: John Hubbard <jhubbard@nvidia.com>

[ Upstream commit 64801d19eba156170340c76f70ade743defcb8ce ]

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.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Keith Busch <keith.busch@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/testing/selftests/vm/gup_benchmark.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/gup_benchmark.c b/tools/testing/selftests/vm/gup_benchmark.c
index c0534e298b512..8e9929ce64cdb 100644
--- a/tools/testing/selftests/vm/gup_benchmark.c
+++ b/tools/testing/selftests/vm/gup_benchmark.c
@@ -71,7 +71,7 @@ int main(int argc, char **argv)
flags |= MAP_SHARED;
break;
case 'H':
- flags |= MAP_HUGETLB;
+ flags |= (MAP_HUGETLB | MAP_ANONYMOUS);
break;
default:
return -1;
--
2.20.1