linux-ext4 - Re: [PATCH -v2 1/3] jbd2: Use atomic variables to avoid taking t_handle_lock in jbd2_journal

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Date:	Mon, 9 Aug 2010 15:05:13 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Jan Kara <jack@...e.cz>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	ocfs2-devel@....oracle.com, John Stultz <johnstul@...ibm.com>,
	Keith Maanthey <kmannth@...ibm.com>,
	Eric Whitney <eric.whitney@...com>
Subject: Re: [PATCH -v2 1/3] jbd2: Use atomic variables to avoid taking
 t_handle_lock in jbd2_journal_stop

On Mon, Aug 09, 2010 at 07:02:16PM +0200, Jan Kara wrote:
>         spin_lock(&journal->j_state_lock);
>         spin_lock(&transaction->t_handle_lock);
> -       transaction->t_outstanding_credits -= handle->h_buffer_credits;
> -       transaction->t_updates--;
> -
> -       if (!transaction->t_updates)
> +       atomic_sub(handle->h_buffer_credits,
> +                  &transaction->t_outstanding_credits);
> +       if (atomic_dec_and_test(&transaction->t_updates))
>
> After this a transaction can disappear so subsequent
> __jbd2_log_start_commit shouldn't dereference transaction->t_tid,
> right?

I think it should be ok because we're holding j_state_lock(), so the
transaction can't disappear until we release the j_state_lock.

	    	  	    	     	     	 - Ted
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