linux-ext4 - Re: [PATCH 00/10] ext4: fix inconsistency since reading old metadata from disk

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Date:   Wed, 10 Jun 2020 18:27:15 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>, "zhangyi (F)" <yi.zhang@...wei.com>,
        linux-ext4@...r.kernel.org, adilger.kernel@...ger.ca,
        zhangxiaoxu5@...wei.com
Subject: Re: [PATCH 00/10] ext4: fix inconsistency since reading old metadata
 from disk

On Wed 10-06-20 11:45:43, Theodore Y. Ts'o wrote:
> On Wed, Jun 10, 2020 at 11:57:39AM +0200, Jan Kara wrote:
> > > So I guess it may still lead to inconsistency. How about add this checking
> > > into ext4_journal_get_write_access() ?
> > 
> > Yes, this also occured to me later. Adding the check to
> > ext4_journal_get_write_access() should be safer.
> 
> There's another thing which we could do.  One of the issues is that we
> allow buffered writeback for block devices once the change to the
> block has been committed.  What if we add a change to block device
> writeback code and in fs/buffer.c so that optionally, the file system
> can specify a callback function can get called when an I/O error has
> been reflected back up from the block layer?
> 
> It seems unfortunate that currently, we can immediately report the I/O
> error for buffered writes to *files*, but for metadata blocks, we
> would only be able to report the problem when we next try to modify
> it.
> 
> Making changes to fs/buffer.c might be controversial, but I think it
> might be result in a better solution.

Yeah, what you propose certainly makes sence could be relatively easily
done by blkdev_writepage() using __block_write_full_page() with appropriate
endio handler which calls fs callback. I'm just not sure how propagate the
callback function from the fs to the blkdev...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR