Re: [PATCH] coda: kill file_count abuse

[Al Viro <viro@ftp.linux.org.uk>]

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.