commit f81cd178ecfd0806c1d2859cfe0a162d80c81a69
author John Hubbard <jhubbard@nvidia.com> Wed Jun 03 15:56:40 2020 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Wed Jun 03 20:09:42 2020 -0700
tree 7abc36f482d48e1add0a8a9a573be4bebd167417
parent 2170ecfa768850bb29487baa3101c993ab7d7402

mm/gup: might_lock_read(mmap_sem) in get_user_pages_fast()

Instead of scattering these assertions across the drivers, do this
assertion inside the core of get_user_pages_fast*() functions.  That also
includes pin_user_pages_fast*() routines.

Add a might_lock_read(mmap_sem) call to internal_get_user_pages_fast().

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Link: http://lkml.kernel.org/r/20200522010443.1290485-1-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup.c

diff --git a/mm/gup.c b/mm/gup.c
index 0702c1a..61ee405 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2739,6 +2739,9 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
 				       FOLL_FAST_ONLY)))
 		return -EINVAL;
 
+	if (!(gup_flags & FOLL_FAST_ONLY))
+		might_lock_read(&current->mm->mmap_sem);
+
 	start = untagged_addr(start) & PAGE_MASK;
 	addr = start;
 	len = (unsigned long) nr_pages << PAGE_SHIFT;