linux-kernel - Re: [RFC][PATCH] Possible data integrity problems in lots of filesystems?

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Date:	Thu, 25 Nov 2010 14:18:30 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Nick Piggin <npiggin@...nel.dk>
CC:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, Roman Zippel <zippel@...ux-m68k.org>,
	"Tigran A. Aivazian" <tigran@...azian.fsnet.co.uk>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Bob Copeland <me@...copeland.com>,
	reiserfs-devel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Evgeniy Dushistov <dushistov@...l.ru>, Jan Kara <jack@...e.cz>
Subject: Re: [RFC][PATCH] Possible data integrity problems in lots of filesystems?

On 11/25/2010 01:47 PM, Nick Piggin wrote:
> On Thu, Nov 25, 2010 at 12:51:11PM +0200, Boaz Harrosh wrote:
> 
> It does not get it right, because of the situation I described
> above. Background writeout can come in first, and clear the inode
> dirty bits, and call your ->write_inode for async writeout.
> 
> That means you skip doing the exofs_put_io_state(), and (I presume)
> this means you aren't waiting for write completion there.
> 
> What then happens is that sync_inode_metadata() from your fsync
> does not call ->write_inode because the inode dirty bits are clear.
> It's basically a noop. So you need to either make your .write_inode
> always synchronous, or wait for it in your .fsync and .sync_fs.
> 

Rrr I now see what you mean, that the previous call to
writeback_single_inode(wait==0) came and go without actually
finishing because exofs_write_inode(wait==0).

So I wish there was an
write_inode_async_done() that will actually do the final inode_sync_complete
or something like that, right? (That I could call from exofs::updatei_done)

Sigh. I think I'll go with the always wait==1 at exofs_write_inode() for
now. Just as your patch.

If there is nothing better by the next Kernel I might consider my own
wait_event() in exofs_file_fsync()

ACK-by: Boaz Harrosh <bharrosh@...asas.com>

Thanks
Boaz
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