ext4: fix partial page writes

While running extended fsx tests to verify the preceeding patches,
a similar bug was also found in the write operation

When ever a write operation begins or ends in a hole,
or extends EOF, the partial page contained in the hole
or beyond EOF needs to be zeroed out.

To correct this the new ext4_discard_partial_page_buffers_no_lock
routine is used to zero out the partial page, but only for buffer
heads that are already unmapped.

Signed-off-by: Allison Henderson <achender@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index f86b149fb8b10e19f2850e08799aaca6087b5d44..6ecc93979e48168d5d62f98de49445152f74a58b 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2255,6 +2255,7 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
        pgoff_t index;
        struct inode *inode = mapping->host;
        handle_t *handle;
+       loff_t page_len;
 
        index = pos >> PAGE_CACHE_SHIFT;
 
@@ -2301,6 +2302,13 @@ retry:
                 */
                if (pos + len > inode->i_size)
                        ext4_truncate_failed_write(inode);
+       } else {
+               page_len = pos & (PAGE_CACHE_SIZE - 1);
+               if (page_len > 0) {
+                       ret = ext4_discard_partial_page_buffers_no_lock(handle,
+                               inode, page, pos - page_len, page_len,
+                               EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED);
+               }
        }
 
        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
@@ -2343,6 +2351,7 @@ static int ext4_da_write_end(struct file *file,
        loff_t new_i_size;
        unsigned long start, end;
        int write_mode = (int)(unsigned long)fsdata;
+       loff_t page_len;
 
        if (write_mode == FALL_BACK_TO_NONDELALLOC) {
                if (ext4_should_order_data(inode)) {
@@ -2391,6 +2400,16 @@ static int ext4_da_write_end(struct file *file,
        }
        ret2 = generic_write_end(file, mapping, pos, len, copied,
                                                        page, fsdata);
+
+       page_len = PAGE_CACHE_SIZE -
+                       ((pos + copied - 1) & (PAGE_CACHE_SIZE - 1));
+
+       if (page_len > 0) {
+               ret = ext4_discard_partial_page_buffers_no_lock(handle,
+                       inode, page, pos + copied - 1, page_len,
+                       EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED);
+       }
+
        copied = ret2;
        if (ret2 < 0)
                ret = ret2;