Subject: Re: EXT3: problem with copy_from_user inside a transaction
From: Chris Mason <mason@suse.com>
To: Andrey Savochkin <saw@saw.sw.com.sg>
Cc: Andrea Arcangeli <andrea@suse.de>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org
In-Reply-To: <20040903175728.C1834@castle.nmd.msu.ru>
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Date: Sat, 04 Sep 2004 03:47:44 -0400
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On Fri, 2004-09-03 at 09:57, Andrey Savochkin wrote:

> > This would mean that all the work is done during the commit_write
> > stage.  The trick is that we would have to handle -ENOSPC since we might
> > not know we've run out of room until after the data has been copied from
> > userland.
> 
> What is the problem -ENOSPC?
> Do you think about the problem of the page existing before this write, it's
> content overwritten, but the filesystem being unable to commit that write
> because it needs more space?

Exactly.  In this case, we've effectively corrupted the page cache. 
We've copied data in that isn't (and never will be) reflected on disk. 
It isn't a horribly difficult case, we just need to overwrite the data
with zeros, making sure to only overwrite the data corresponding to the
-ENOSPC error.

-chris


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