linux-ext4 - Re: [PATCH 1/3] jbd2,rcu: correctly use RCU

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Message-ID: <20110711012429.GD28763@thunk.org>
Date:	Sun, 10 Jul 2011 21:24:29 -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>

Actually, after thinking about this some more, I think I'm going to
just change the jbd2 events to simply print MAJOR(__entry->dev) and
MINOR(__entry->dev).  Otherwise, the perf tool stops dies and stops
interpreting the trace points when it tries to interpret
"jbd2_dev_to_name(REC->dev)" in the print format.

So I'll just drop jbd2_dev_to_name() completely for the jbd2
tracepoints.  It's not worth it.

	      				- Ted
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