[PATCH AUTOSEL 4.19 05/43] 9p: avoid attaching writeback_fid on mmap with type PRIVATE

Sasha Levin
2019-10-01T16:54:03Z

From: Chengguang Xu <cgxu519@zoho.com.cn>

[ 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@zoho.com.cn
Signed-off-by: Chengguang Xu <cgxu519@zoho.com.cn>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 05454a7e22dc2..550d0b169d7c2 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