From: Allison Henderson <achender@linux.vnet.ibm.com>
Date: Mon, 22 Aug 2011 19:06:53 +0000 (-0400)
Subject: ext4: fix partial page writes
X-Git-Tag: next-20110824~74^2
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=aefd045e1b15cb179ce43ac4a76dcd711b10a684;p=karo-tx-linux.git

ext4: fix partial page writes

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>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index e908788ec386..c3ce7547e315 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2258,6 +2258,7 @@ 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;
 
@@ -2304,6 +2305,11 @@ 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))
@@ -2346,6 +2352,7 @@ 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)) {
@@ -2394,6 +2401,14 @@ 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;