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Date:   Tue, 21 May 2019 12:59:28 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     David Howells <dhowells@redhat.com>,
        Christian Brauner <christian@brauner.io>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
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Subject: Re: [PATCH 1/2] open: add close_range()
Message-ID: <20190521195928.GB6738@bombadil.infradead.org>
References: <20190521150006.GJ17978@ZenIV.linux.org.uk>
 <20190521113448.20654-1-christian@brauner.io>
 <28114.1558456227@warthog.procyon.org.uk>
 <20190521192009.GK17978@ZenIV.linux.org.uk>
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On Tue, May 21, 2019 at 08:20:09PM +0100, Al Viro wrote:
> On Tue, May 21, 2019 at 05:30:27PM +0100, David Howells wrote:
> 
> > If we can live with close_from(int first) rather than close_range(), then this
> > can perhaps be done a lot more efficiently by:
> > 
> > 	new = alloc_fdtable(first);
> > 	spin_lock(&files->file_lock);
> > 	old = files_fdtable(files);
> > 	copy_fds(new, old, 0, first - 1);
> > 	rcu_assign_pointer(files->fdt, new);
> > 	spin_unlock(&files->file_lock);
> > 	clear_fds(old, 0, first - 1);
> > 	close_fdt_from(old, first);
> > 	kfree_rcu(old);
> 
> I really hate to think how that would interact with POSIX locks...

POSIX locks store current->files in fl_owner; David's resizing the
underlying files->fdt, just like growing from 64 to 256 fds.