From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ftp.linux.org.uk>
Subject: Re: [PATCH] coda: kill file_count abuse
Date: Fri, 20 Jul 2007 01:53:16 +0100
Message-ID: <20070720005316.GA21668@ftp.linux.org.uk>
References: <20070719214508.GA4482@lst.de> <20070719221559.GI8857@delft.aura.cs.cmu.edu> <20070720004534.GA31489@sgi.com>
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Cc: Christoph Hellwig <hch@lst.de>, akpm@osdl.org,
	linux-fsdevel@vger.kernel.org
To: David Chinner <dgc@sgi.com>
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On Fri, Jul 20, 2007 at 10:45:34AM +1000, David Chinner wrote:
> On Thu, Jul 19, 2007 at 06:16:00PM -0400, Jan Harkes wrote:
> > On Thu, Jul 19, 2007 at 11:45:08PM +0200, Christoph Hellwig wrote:
> > > ->release is the proper way to detect the last close of a file,
> > > file_count should never be used in filesystems.
> > 
> > Has been tried, the problem with that once ->release is called it is too
> > late to pass the the error back to close(2).
> 
> I think you'll find the problem is that fput() throws away the error
> from ->release, not that it's too late....

Just where would that return value go?

BTW, the reason why checks for struct file refcount blow is not far
from that:

task A: write()
task B (sharing descriptor table with A): close()
task C (with another reference to struct file in question): close()
task A: return from write()

Now, the final fput() here happens in write().  In particular, no
call of close(2) sees refcount equal to 1.