[PATCH] retries in ext4_prepare_write() violate ordering requirements

In journal=ordered or journal=data mode retry in ext4_prepare_write()
breaks the requirements of journaling of data with respect to metadata.
The fix is to call commit_write to commit allocated zero blocks before
retry.

Signed-off-by: Kirill Korotaev <dev@openvz.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Ken Chen <kenneth.w.chen@intel.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 75 insertions, 10 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0a60ec5a16d..1d85d4ec959 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1147,37 +1147,102 @@ static int do_journal_get_write_access(handle_t *handle,
         return ext4_journal_get_write_access(handle, bh);
 }
 
+/*
+ * The idea of this helper function is following:
+ * if prepare_write has allocated some blocks, but not all of them, the
+ * transaction must include the content of the newly allocated blocks.
+ * This content is expected to be set to zeroes by block_prepare_write().
+ * 2006/10/14  SAW
+ */
+static int ext4_prepare_failure(struct file *file, struct page *page,
+                                unsigned from, unsigned to)
+{
+        struct address_space *mapping;
+        struct buffer_head *bh, *head, *next;
+        unsigned block_start, block_end;
+        unsigned blocksize;
+        int ret;
+        handle_t *handle = ext4_journal_current_handle();
+
+        mapping = page->mapping;
+        if (ext4_should_writeback_data(mapping->host)) {
+                /* optimization: no constraints about data */
+skip:
+                return ext4_journal_stop(handle);
+        }
+
+        head = page_buffers(page);
+        blocksize = head->b_size;
+        for (   bh = head, block_start = 0;
+                bh != head || !block_start;
+                block_start = block_end, bh = next)
+        {
+                next = bh->b_this_page;
+                block_end = block_start + blocksize;
+                if (block_end <= from)
+                        continue;
+                if (block_start >= to) {
+                        block_start = to;
+                        break;
+                }
+                if (!buffer_mapped(bh))
+                /* prepare_write failed on this bh */
+                        break;
+                if (ext4_should_journal_data(mapping->host)) {
+                        ret = do_journal_get_write_access(handle, bh);
+                        if (ret) {
+                                ext4_journal_stop(handle);
+                                return ret;
+                        }
+                }
+        /*
+         * block_start here becomes the first block where the current iteration
+         * of prepare_write failed.
+         */
+        }
+        if (block_start <= from)
+                goto skip;
+
+        /* commit allocated and zeroed buffers */
+        return mapping->a_ops->commit_write(file, page, from, block_start);
+}
+
 static int ext4_prepare_write(struct file *file, struct page *page,
                               unsigned from, unsigned to)
 {
         struct inode *inode = page->mapping->host;
-        int ret, needed_blocks = ext4_writepage_trans_blocks(inode);
+        int ret, ret2;
+        int needed_blocks = ext4_writepage_trans_blocks(inode);
         handle_t *handle;
         int retries = 0;
 
 retry:
         handle = ext4_journal_start(inode, needed_blocks);
-        if (IS_ERR(handle)) {
-                ret = PTR_ERR(handle);
-                goto out;
-        }
+        if (IS_ERR(handle))
+                return PTR_ERR(handle);
         if (test_opt(inode->i_sb, NOBH) && ext4_should_writeback_data(inode))
                 ret = nobh_prepare_write(page, from, to, ext4_get_block);
         else
                 ret = block_prepare_write(page, from, to, ext4_get_block);
         if (ret)
-                goto prepare_write_failed;
+                goto failure;
 
         if (ext4_should_journal_data(inode)) {
                 ret = walk_page_buffers(handle, page_buffers(page),
                                 from, to, NULL, do_journal_get_write_access);
+                if (ret)
+                        /* fatal error, just put the handle and return */
+                        journal_stop(handle);
         }
-prepare_write_failed:
-        if (ret)
-                ext4_journal_stop(handle);
+        return ret;
+
+failure:
+        ret2 = ext4_prepare_failure(file, page, from, to);
+        if (ret2 < 0)
+                return ret2;
         if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                 goto retry;
-out:
+        /* retry number exceeded, or other error like -EDQUOT */
         return ret;
 }