linux-kernel - Re: [PATCH 03/11] ftrace: Cleanup regex_lock and ftrace

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Date:	Thu, 09 May 2013 18:09:04 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com, Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Tom Zanussi <tom.zanussi@...el.com>
Subject: Re: [PATCH 03/11] ftrace: Cleanup regex_lock and ftrace_lock around
 hash updating

On Thu, 2013-05-09 at 13:12 -0400, Steven Rostedt wrote:
> On Thu, 2013-05-09 at 14:44 +0900, Masami Hiramatsu wrote:
> > Cleanup regex_lock and ftrace_lock locking points around
> > ftrace_ops hash update code.
> > 
> > The new rule is that regex_lock protects ops->*_hash
> > read-update-write code for each ftrace_ops. Usually,
> > hash update is done by following sequence.
> > 
> > 1. allocate a new local hash and copy the original hash.
> > 2. update the local hash.
> > 3. move(actually, copy) back the local hash to ftrace_ops.
> > 4. update ftrace entries if needed.
> > 5. release the local hash.
> > 
> > This makes regex_lock to protect #1-#4, and ftrace_lock
> > to protect #3 and #4.
> 
> Patch looks good, but I don't see how ftrace_lock protects #3. The two
> things that I see ftrace_lock protecting is the update to the ftrace
> entries, and the adding and removing ftrace_ops to the ftrace_ops_list.

OK, yeah, the move does an implicit entries update. Thus it does need
the lock. I'll update the change log to imply that.

-- Steve


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