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Message-id: <7A65EEA3-78FD-49C3-B683-265B93F8AC96@sun.com>
Date: Tue, 01 Dec 2009 15:02:04 -0700
From: Andreas Dilger <adilger@....com>
To: Jan Kara <jack@...e.cz>
Cc: Mike Galbraith <gleep@....de>, James Y Knight <foom@...m.net>,
ext4 development <linux-ext4@...r.kernel.org>, npiggin@...e.de
Subject: Re: writev data loss bug in (at least) 2.6.31 and 2.6.32pre8 x86-64
On 2009-12-01, at 09:03, Jan Kara wrote:
> On Tue 01-12-09 15:35:59, Jan Kara wrote:
>> On Tue 01-12-09 12:42:45, Mike Galbraith wrote:
>>> On Mon, 2009-11-30 at 19:48 -0500, James Y Knight wrote:
>>>> On Nov 30, 2009, at 3:55 PM, James Y Knight wrote:
>>>>> This test case is distilled from an actual application which
>>>>> doesn't even intentionally use writev: it just uses C++'s
>>>>> ofstream class to write data to a file. Unfortunately, that
>>>>> class smart and uses writev under the covers. Unfortunately, I
>>>>> guess nobody ever tests linux writev behavior, since it's broken
>>>>> _so_much_of_the_time_. I really am quite astounded to see such a
>>>>> bad track record for such a fundamental core system call....
I suspect an excellent way of exposing problems with the writev()
interface would be to wire it into fsx, which is commonly run as a
stress test for Linux. I don't know if it would have caught this
case, but it definitely couldn't hurt to get more testing cycles for it.
>> Ext4 also has this problem but delayed allocation mitigates the
>> effect to an error in accounting of blocks reserved for delayed
>> allocation and thus under normal circumstances nothing bad happens.
It looks like ext4 might still hit this problem, if delalloc is
disabled. Could you please submit a similar patch for ext4 also.
> The patch below fixes the issue for me...
>
> Honza
>
> From 1b2ad411dd86afbfdb3c5b0f913230e9f1f0b858 Mon Sep 17 00:00:00 2001
> From: Jan Kara <jack@...e.cz>
> Date: Tue, 1 Dec 2009 16:53:06 +0100
> Subject: [PATCH] ext3: Fix data / filesystem corruption when write
> fails to copy data
>
> When ext3_write_begin fails after allocating some blocks or
> generic_perform_write fails to copy data to write, we truncate
> blocks already instantiated beyond i_size. Although these blocks
> were never inside i_size, we have to truncate pagecache of these
> blocks so that corresponding buffers get unmapped. Otherwise
> subsequent __block_prepare_write (called because we are retrying the
> write) will find the buffers mapped, not call ->get_block, and thus
> the page will be backed by already freed blocks leading to
> filesystem and data corruption.
>
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
> fs/ext3/inode.c | 18 ++++++++++++++----
> 1 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
> index 354ed3b..f9d6937 100644
> --- a/fs/ext3/inode.c
> +++ b/fs/ext3/inode.c
> @@ -1151,6 +1151,16 @@ static int
> do_journal_get_write_access(handle_t *handle,
> return ext3_journal_get_write_access(handle, bh);
> }
>
> +/*
> + * Truncate blocks that were not used by write. We have to truncate
> the
> + * pagecache as well so that corresponding buffers get properly
> unmapped.
> + */
> +static void ext3_truncate_failed_write(struct inode *inode)
> +{
> + truncate_inode_pages(inode->i_mapping, inode->i_size);
> + ext3_truncate(inode);
> +}
> +
> static int ext3_write_begin(struct file *file, struct address_space
> *mapping,
> loff_t pos, unsigned len, unsigned flags,
> struct page **pagep, void **fsdata)
> @@ -1209,7 +1219,7 @@ write_begin_failed:
> unlock_page(page);
> page_cache_release(page);
> if (pos + len > inode->i_size)
> - ext3_truncate(inode);
> + ext3_truncate_failed_write(inode);
> }
> if (ret == -ENOSPC && ext3_should_retry_alloc(inode->i_sb, &retries))
> goto retry;
> @@ -1304,7 +1314,7 @@ static int ext3_ordered_write_end(struct file
> *file,
> page_cache_release(page);
>
> if (pos + len > inode->i_size)
> - ext3_truncate(inode);
> + ext3_truncate_failed_write(inode);
> return ret ? ret : copied;
> }
>
> @@ -1330,7 +1340,7 @@ static int ext3_writeback_write_end(struct
> file *file,
> page_cache_release(page);
>
> if (pos + len > inode->i_size)
> - ext3_truncate(inode);
> + ext3_truncate_failed_write(inode);
> return ret ? ret : copied;
> }
>
> @@ -1383,7 +1393,7 @@ static int ext3_journalled_write_end(struct
> file *file,
> page_cache_release(page);
>
> if (pos + len > inode->i_size)
> - ext3_truncate(inode);
> + ext3_truncate_failed_write(inode);
> return ret ? ret : copied;
> }
>
> --
> 1.6.4.2
>
> --
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Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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