linux-kernel - Re: [PATCH 1/3] jbd2,rcu: correctly use RCU

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Message-ID: <20110711002502.GC28763@thunk.org>
Date:	Sun, 10 Jul 2011 20:25:02 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] jbd2,rcu: correctly use RCU

On Thu, Jun 16, 2011 at 09:47:04AM +0800, Lai Jiangshan wrote:
> In read site, we need to use local_ptr = rcu_dereference(),
> and then use this local_ptr to read the content.
> 
> In update site, we should assign/publish the new object/pointer after
> the content of the new object/pointer is fully initialized,
> and we can't not touch the object after the pointer assignment.
> rcu_assign_pointer() is need for the assignement.
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>

Thanks, applied.

> @@ -2447,24 +2447,25 @@ const char *jbd2_dev_to_name(dev_t device)
>  	int	i = hash_32(device, CACHE_SIZE_BITS);
>  	char	*ret;
>  	struct block_device *bd;
> -	static struct devname_cache *new_dev;
> +	static struct devname_cache *cache;

I also removed the static modifier to the struct devname_cache
pointer.  It's pointless, and in fact introduces a bug if two CPU's
try to run jbd2_dev_to_name() at the same time.

						- Ted
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