[JFFS2] Fix return value from jffs2_write_end()

jffs2_write_end() is sometimes passing back a "written" length greater 
than the length we passed into it, leading to a BUG at mm/filemap.c:1749 
when used with unionfs.

It happens because we actually write more than was requested, to reduce 
log fragmentation. These "longer" writes are fine, but they shouldn't 
get propagated back to the vm/vfs.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

1 files changed, 4 insertions, 7 deletions

diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c
index 023a17539dd..f9c5dd6f4b6 100644
--- a/fs/jffs2/file.c
+++ b/fs/jffs2/file.c
@@ -255,7 +255,7 @@ static int jffs2_write_end(struct file *filp, struct address_space *mapping,
                    _whole_ page. This helps to reduce the number of
                    nodes in files which have many short writes, like
                    syslog files. */
-                start = aligned_start = 0;
+                aligned_start = 0;
         }
 
         ri = jffs2_alloc_raw_inode();
@@ -291,14 +291,11 @@ static int jffs2_write_end(struct file *filp, struct address_space *mapping,
         }
 
         /* Adjust writtenlen for the padding we did, so we don't confuse our caller */
-        if (writtenlen < (start&3))
-                writtenlen = 0;
-        else
-                writtenlen -= (start&3);
+        writtenlen -= min(writtenlen, (start - aligned_start));
 
         if (writtenlen) {
-                if (inode->i_size < (pg->index << PAGE_CACHE_SHIFT) + start + writtenlen) {
-                        inode->i_size = (pg->index << PAGE_CACHE_SHIFT) + start + writtenlen;
+                if (inode->i_size < pos + writtenlen) {
+                        inode->i_size = pos + writtenlen;
                         inode->i_blocks = (inode->i_size + 511) >> 9;
 
                         inode->i_ctime = inode->i_mtime = ITIME(je32_to_cpu(ri->ctime));