[CIFS] cifs_prepare_write was incorrectly rereading page in some cases

Noticed by Shaggy.

Signed-off-by: Shaggy <shaggy@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 40 insertions, 22 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index c07ff8317a8b..2d3275bedb55 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1992,34 +1992,52 @@ static int cifs_prepare_write(struct file *file, struct page *page,
         unsigned from, unsigned to)
 {
         int rc = 0;
-        loff_t offset = (loff_t)page->index << PAGE_CACHE_SHIFT;
+        loff_t i_size;
+        loff_t offset;
+
         cFYI(1, ("prepare write for page %p from %d to %d",page,from,to));
-        if (!PageUptodate(page)) {
-        /*      if (to - from != PAGE_CACHE_SIZE) {
-                        void *kaddr = kmap_atomic(page, KM_USER0);
+        if (PageUptodate(page))
+                return 0;
+
+        /* If we are writing a full page it will be up to date,
+           no need to read from the server */
+        if ((to == PAGE_CACHE_SIZE) && (from == 0)) {
+                SetPageUptodate(page);
+                return 0;
+        }
+
+        offset = (loff_t)page->index << PAGE_CACHE_SHIFT;
+        i_size = i_size_read(page->mapping->host);
+
+        if ((offset >= i_size) ||
+            ((from == 0) && (offset + to) >= i_size)) {
+                /*
+                 * We don't need to read data beyond the end of the file.
+                 * zero it, and set the page uptodate
+                 */
+                void *kaddr = kmap_atomic(page, KM_USER0);
+
+                if (from)
                         memset(kaddr, 0, from);
+                if (to < PAGE_CACHE_SIZE)
                         memset(kaddr + to, 0, PAGE_CACHE_SIZE - to);
-                        flush_dcache_page(page);
-                        kunmap_atomic(kaddr, KM_USER0);
-                } */
-                /* If we are writing a full page it will be up to date,
-                   no need to read from the server */
-                if ((to == PAGE_CACHE_SIZE) && (from == 0))
-                        SetPageUptodate(page);
-
+                flush_dcache_page(page);
+                kunmap_atomic(kaddr, KM_USER0);
+                SetPageUptodate(page);
+        } else if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
                 /* might as well read a page, it is fast enough */
-                if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
-                        rc = cifs_readpage_worker(file, page, &offset);
-                } else {
-                /* should we try using another file handle if there is one -
-                   how would we lock it to prevent close of that handle
-                   racing with this read?
-                   In any case this will be written out by commit_write */
-                }
+                rc = cifs_readpage_worker(file, page, &offset);
+        } else {
+                /* we could try using another file handle if there is one -
+                   but how would we lock it to prevent close of that handle
+                   racing with this read? In any case
+                   this will be written out by commit_write so is fine */
         }
 
-        /* BB should we pass any errors back? 
-           e.g. if we do not have read access to the file */
+        /* we do not need to pass errors back 
+           e.g. if we do not have read access to the file 
+           because cifs_commit_write will do the right thing.  -- shaggy */
+
         return 0;
 }