[PATCH 6/6 v5] ext4: fix partial page writes

[Allison Henderson <achender@linux.vnet.ibm.com>]

These bugs were also found during extended fsx testing
for blocksize = 1k.

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>
---
:100644 100644 c1b42cb... 78c723b... M	fs/ext4/inode.c
 fs/ext4/inode.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c1b42cb..78c723b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2214,6 +2214,7 @@ 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;
 
@@ -2260,6 +2261,11 @@ retry:
 		 */
 		if (pos + len > inode->i_size)
 			ext4_truncate_failed_write(inode);
+	} else {
+		page_len = pos & (PAGE_CACHE_SIZE - 1);
+		ext4_discard_partial_page_buffers_no_lock(handle,
+			inode, page, pos - page_len, page_len,
+			EXT4_DSCRD_PARTIAL_PG_ZERO_UNMAPED);
 	}
 
 	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
@@ -2302,6 +2308,7 @@ 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)) {
@@ -2350,6 +2357,14 @@ 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) & (PAGE_CACHE_SIZE - 1));
+
+	ext4_discard_partial_page_buffers_no_lock(handle,
+		inode, page, pos + copied, page_len,
+		EXT4_DSCRD_PARTIAL_PG_ZERO_UNMAPED);
+
 	copied = ret2;
 	if (ret2 < 0)
 		ret = ret2;
-- 
1.7.1