From: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue, 30 Aug 2016 02:39:56 +0000 (-0400)
Subject: simple_write_end(): don't zero in short copy into uptodate
X-Git-Tag: v4.10-rc1~57^2~2^2
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=04fff6416cb7876091f0b2f413caf43e3618d5ad;p=karo-tx-linux.git

simple_write_end(): don't zero in short copy into uptodate

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---

diff --git a/fs/libfs.c b/fs/libfs.c
index 48826d4da189..76048705d922 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -465,6 +465,8 @@ EXPORT_SYMBOL(simple_write_begin);
  * is not called, so a filesystem that actually does store data in .write_inode
  * should extend on what's done here with a call to mark_inode_dirty() in the
  * case that i_size has changed.
+ *
+ * Use *ONLY* with simple_readpage()
  */
 int simple_write_end(struct file *file, struct address_space *mapping,
 			loff_t pos, unsigned len, unsigned copied,
@@ -474,14 +476,14 @@ int simple_write_end(struct file *file, struct address_space *mapping,
 	loff_t last_pos = pos + copied;
 
 	/* zero the stale part of the page if we did a short copy */
-	if (copied < len) {
-		unsigned from = pos & (PAGE_SIZE - 1);
-
-		zero_user(page, from + copied, len - copied);
-	}
+	if (!PageUptodate(page)) {
+		if (copied < len) {
+			unsigned from = pos & (PAGE_SIZE - 1);
 
-	if (!PageUptodate(page))
+			zero_user(page, from + copied, len - copied);
+		}
 		SetPageUptodate(page);
+	}
 	/*
 	 * No need to use i_size_read() here, the i_size
 	 * cannot change under us because we hold the i_mutex.