linux-ext4 - Re: [PATCH 2/2 take2] jbd2: delete spin_lock(t_handle_lock) inside wirte_lock(j_state

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Message-ID: <20120105032754.GD24494@thunk.org>
Date:	Wed, 4 Jan 2012 22:27:54 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
Cc:	adilger.kernel@...ger.ca, Yongqiang Yang <xiaoqiangnk@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2 take2] jbd2: delete spin_lock(t_handle_lock) inside
 wirte_lock(j_state_lock)

On Mon, Dec 26, 2011 at 10:17:27AM +0900, Toshiyuki Okajima wrote:
> Delete all spin_lock(t_handle_lock) statements inside write_lock(j_state_lock) 
> because the critical code sections can be protected by write_lock(j_state_lock)
> only.
> 
> Signed-off-by: Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
> Reported-by: Yongqiang Yang <xiaoqiangnk@...il.com>

This may be true today, but I'm worried this is going to make the code
more fragile.  The header file include/linux/jbd2.h defines which
fields are protected by which lock.  This patch is going to make those
comments partially obsolete.  We need to make sure the locking
protocol is clearly defined before we go around removing locks.

This is something I would like to do, but we need to make sure the
code remains maintainable in the long run.

					- Ted
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