linux-kernel - Re: [PATCH 1/2] open: add close

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Message-ID: <20190521195928.GB6738@bombadil.infradead.org>
Date:   Tue, 21 May 2019 12:59:28 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     David Howells <dhowells@...hat.com>,
        Christian Brauner <christian@...uner.io>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, jannh@...gle.com, fweimer@...hat.com,
        oleg@...hat.com, tglx@...utronix.de, torvalds@...ux-foundation.org,
        arnd@...db.de, shuah@...nel.org, tkjos@...roid.com,
        ldv@...linux.org, miklos@...redi.hu, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH 1/2] open: add close_range()

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.