Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
WARN_ON_ONCE and returning an error. This is to ensure users of the
vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
and get an indication of an error without panicing the kernel.
This will help identifying drivers that need to clear VM_PFNMAP before
using dmabuf system heap which is moving to use vm_insert_page.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index feff48e1465a..e503c9801cd9 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
 		return -EINVAL;
 	if (!(vma->vm_flags & VM_MIXEDMAP)) {
 		BUG_ON(mmap_read_trylock(vma->vm_mm));