[PATCH] mm: Release a semaphore in 'get_vaddr_frames()'

[Christophe JAILLET]

A semaphore is acquired before this check, so we must release it before
leaving.

Fixes: b7f0554a56f2 ("mm: fail get_vaddr_frames() for filesystem-dax mappings")
Signed-off-by: Christophe JAILLET <christophe.jail...@wanadoo.fr>
---
-- Untested --

The wording of the commit entry and log description could be improved
but I didn't find something better.
---
 mm/frame_vector.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 297c7238f7d4..e0c5e659fa82 100644
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -62,8 +62,10 @@ int get_vaddr_frames(unsigned long start, unsigned int 
nr_frames,
         * get_user_pages_longterm() and disallow it for filesystem-dax
         * mappings.
         */
-       if (vma_is_fsdax(vma))
+       if (vma_is_fsdax(vma)) {
+               up_read(&mm->mmap_sem);
                return -EOPNOTSUPP;
+       }
 
        if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
                vec->got_ref = true;
-- 
2.14.1