On Tue, 01 Dec 2009 15:02:04 -0700 Andreas Dilger wrote: > 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. Maybe someone from LTP would be interested in adding this test functionality to fsx-linux ? Source/test program is available at http://marc.info/?l=linux-kernel&m=125961612418323&w=2 > >> 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@xxxxxxx> > > 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@xxxxxxx> > > --- > > 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; > > } > > > > -- > > Cheers, Andreas > -- > Andreas Dilger > Sr. Staff Engineer, Lustre Group > Sun Microsystems of Canada, Inc. --- ~Randy -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
