fuse: fix fuse_write_end() if zero bytes were copied

commit 59c3b76cc61d1d676f965c192cc7969aa5cb2744 upstream.

If pos is at the beginning of a page and copied is zero then page is not
zeroed but is marked uptodate.

Fix by skipping everything except unlock/put of page if zero bytes were
copied.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: 6b12c1b37e55 ("fuse: Implement write_begin/write_end callbacks")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index a1760776a1221a6cf7d0b63b3c9fdc3466bc2961..4e9cfbc453c75357507736b34a48a8750948c153 100644 (file)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2058,6 +2058,10 @@ static int fuse_write_end(struct file *file, struct address_space *mapping,
 {
        struct inode *inode = page->mapping->host;
 
+       /* Haven't copied anything?  Skip zeroing, size extending, dirtying. */
+       if (!copied)
+               goto unlock;
+
        if (!PageUptodate(page)) {
                /* Zero any unwritten bytes at the end of the page */
                size_t endoff = (pos + copied) & ~PAGE_CACHE_MASK;
@@ -2068,6 +2072,8 @@ static int fuse_write_end(struct file *file, struct address_space *mapping,
 
        fuse_write_update_size(inode, pos + copied);
        set_page_dirty(page);
+
+unlock:
        unlock_page(page);
        page_cache_release(page);