[PATCH 4.9 17/92] 9p: avoid attaching writeback_fid on mmap with type PRIVATE

[Greg Kroah-Hartman]

From: Chengguang Xu <cgxu519@xxxxxxxxxxx>

[ Upstream commit c87a37ebd40b889178664c2c09cc187334146292 ]

Currently on mmap cache policy, we always attach writeback_fid
whether mmap type is SHARED or PRIVATE. However, in the use case
of kata-container which combines 9p(Guest OS) with overlayfs(Host OS),
this behavior will trigger overlayfs' copy-up when excute command
inside container.

Link: http://lkml.kernel.org/r/20190820100325.10313-1-cgxu519@xxxxxxxxxxx
Signed-off-by: Chengguang Xu <cgxu519@xxxxxxxxxxx>
Signed-off-by: Dominique Martinet <dominique.martinet@xxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/9p/vfs_file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 79ff727254bb6..e963b83afc717 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -528,6 +528,7 @@ v9fs_mmap_file_mmap(struct file *filp, struct vm_area_struct *vma)
 	v9inode = V9FS_I(inode);
 	mutex_lock(&v9inode->v_mutex);
 	if (!v9inode->writeback_fid &&
+	    (vma->vm_flags & VM_SHARED) &&
 	    (vma->vm_flags & VM_WRITE)) {
 		/*
 		 * clone a fid and add it to writeback_fid
@@ -629,6 +630,8 @@ static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
 			(vma->vm_end - vma->vm_start - 1),
 	};
 
+	if (!(vma->vm_flags & VM_SHARED))
+		return;
 
 	p9_debug(P9_DEBUG_VFS, "9p VMA close, %p, flushing", vma);
 
-- 
2.20.1