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

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Message-ID: <21839.1308574037@redhat.com>
Date:	Mon, 20 Jun 2011 13:47:17 +0100
From:	David Howells <dhowells@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	dhowells@...hat.com, 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

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.

David
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