Andrew,
Dmitry confirmed that it works in NOBH mode as well
and when quota limit is hit.
Thanks,
Kirill
> Andrew,
>
>
>>>in journal=ordered or journal=data mode retry in ext3_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.
>>>
>>
>>
>>How was this problem detected? (ie: why was block_prepare_write() failing?)
>
> purely theoretically while hunting for other bugs related to ext3 and quota.
> block_prepare_write() can fail e.g. if quota returns -EDQUOT in ext3_alloc_blocks().
>
>
>>How was the patch tested?
>
> 1. it was tested as part of OpenVZ kernel
> 2. there were ext3 stress test done with lots of disk activity by Dmitry Monakhov.
>
>
>>Was nobh-mode also tested?
>
> I will ask to perform some more tests 100% triggering ext3_prepare_failure()
> and with NOBH mode.
>
> Thanks,
> Kirill
>
>
>
>>>--- ./fs/ext3/inode.c.ext3pw 2006-11-08 17:44:14.000000000 +0300
>>>+++ ./fs/ext3/inode.c 2006-11-08 17:48:59.000000000 +0300
>>>@@ -1148,37 +1148,89 @@ static int do_journal_get_write_access(h
>>> return ext3_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 ext3_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;
>>>+
>>>+ mapping = page->mapping;
>>>+ if (ext3_should_writeback_data(mapping->host)) {
>>>+ /* optimization: no constraints about data */
>>>+skip:
>>>+ ext3_journal_stop(ext3_journal_current_handle());
>>>+ return 0;
>>
>>
>>Should this be `return ext3_journal_stop(...);'?
>>
>>
>>
>>>+ }
>>>+
>>>+ 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))
>>>+ break;
>>
>>
>>What is the significance of buffer_mapped() here? Outside EOF or into a
>>hole? If so, then block_start >= to, and we can't get here??
>>
>>
>>
>>>+ }
>>>+ if (block_start <= from)
>>>+ goto skip;
>>>+
>>>+ /* commit allocated and zeroed buffers */
>>>+ return mapping->a_ops->commit_write(file, page, from, block_start);
>>>+}
>>>+
>>>static int ext3_prepare_write(struct file *file, struct page *page,
>>> unsigned from, unsigned to)
>>>{
>>> struct inode *inode = page->mapping->host;
>>>- int ret, needed_blocks = ext3_writepage_trans_blocks(inode);
>>>+ int ret, ret2;
>>>+ int needed_blocks = ext3_writepage_trans_blocks(inode);
>>> handle_t *handle;
>>> int retries = 0;
>>>
>>>retry:
>>> handle = ext3_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) && ext3_should_writeback_data(inode))
>>> ret = nobh_prepare_write(page, from, to, ext3_get_block);
>>> else
>>> ret = block_prepare_write(page, from, to, ext3_get_block);
>>> if (ret)
>>>- goto prepare_write_failed;
>>>+ goto failure;
>>>
>>> if (ext3_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)
>>>- ext3_journal_stop(handle);
>>>+ return ret;
>>>+
>>>+failure:
>>>+ ret2 = ext3_prepare_failure(file, page, from, to);
>>>+ if (ret2 < 0)
>>>+ return ret2;
>>> if (ret == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))
>>> goto retry;
>>>-out:
>>>+ /* retry number exceeded, or other error like -EDQUOT */
>>> return ret;
>>>}
>>>
>>
>>
>
> -
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