fuse: lock page in mkwrite

Lock the page in fuse_page_mkwrite() to protect against a race with
fuse_writepage() where the page is redirtied before the actual writeback
begins.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 9 insertions, 6 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 944acc096752..6fb9425c23c6 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1618,14 +1618,17 @@ static void fuse_vma_close(struct vm_area_struct *vma)
 static int fuse_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
         struct page *page = vmf->page;
-        /*
-         * Don't use page->mapping as it may become NULL from a
-         * concurrent truncate.
-         */
-        struct inode *inode = vma->vm_file->f_mapping->host;
+        struct inode *inode = file_inode(vma->vm_file);
+
+        file_update_time(vma->vm_file);
+        lock_page(page);
+        if (page->mapping != inode->i_mapping) {
+                unlock_page(page);
+                return VM_FAULT_NOPAGE;
+        }
 
         fuse_wait_on_page_writeback(inode, page->index);
-        return 0;
+        return VM_FAULT_LOCKED;
 }
 
 static const struct vm_operations_struct fuse_file_vm_ops = {