linux-kernel - Re: [RFC] get_write_access()/deny_write_access() without inode->i

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Message-ID: <20110620131818.GR11521@ZenIV.linux.org.uk>
Date:	Mon, 20 Jun 2011 14:18:18 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	David Howells <dhowells@...hat.com>
Cc:	linux-arch@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC] get_write_access()/deny_write_access() without
 inode->i_lock

On Mon, Jun 20, 2011 at 01:47:17PM +0100, David Howells wrote:
> Al Viro <viro@...IV.linux.org.uk> wrote:
> 
> > +	for (v = atomic_read(&inode->i_writecount); v >= 0; v = v1) {
> > +		v1 = atomic_cmpxchg(&inode->i_writecount, v, v + 1);
> > +		if (likely(v1 == v))
> > +			return 0;
> > +	}
> 
> You don't need to reissue the atomic_read().  atomic_cmpxchg() returns the
> current value of the memory location.  Just set v to v1 before going round the
> loop again.

That's precisely what that loop is doing...
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