linux-ext4 - Re: [PATCH v3] Updated locking documentation for transaction

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Date:   Wed, 17 Mar 2021 21:58:12 +0100
From:   Alexander Lochmann <alexander.lochmann@...dortmund.de>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Horst Schirmeier <horst.schirmeier@...dortmund.de>,
        Jan Kara <jack@...e.cz>, "Theodore Ts'o" <tytso@....edu>,
        Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] Updated locking documentation for transaction_t

Does this patch look good to you either?

- Alex

On 11.02.21 18:14, Alexander Lochmann wrote:
> Some members of transaction_t are allowed to be read without
> any lock being held if accessed from the correct context.
> We used LockDoc's findings to determine those members.
> Each member of them is marked with a short comment:
> "no lock needed for jbd2 thread".
> 
> Signed-off-by: Alexander Lochmann <alexander.lochmann@...dortmund.de>
> Signed-off-by: Horst Schirmeier <horst.schirmeier@...dortmund.de>
> Reviewed-by: Jan Kara <jack@...e.cz>
> ---
>  include/linux/jbd2.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 99d3cd051ac3..1f19d19f6435 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -594,18 +594,18 @@ struct transaction_s
>  	 */
>  	unsigned long		t_log_start;
>  
> -	/* Number of buffers on the t_buffers list [j_list_lock] */
> +	/* Number of buffers on the t_buffers list [j_list_lock, no locks needed for jbd2 thread] */
>  	int			t_nr_buffers;
>  
>  	/*
>  	 * Doubly-linked circular list of all buffers reserved but not yet
> -	 * modified by this transaction [j_list_lock]
> +	 * modified by this transaction [j_list_lock, no locks needed for jbd2 thread]
>  	 */
>  	struct journal_head	*t_reserved_list;
>  
>  	/*
>  	 * Doubly-linked circular list of all metadata buffers owned by this
> -	 * transaction [j_list_lock]
> +	 * transaction [j_list_lock, no locks needed for jbd2 thread]
>  	 */
>  	struct journal_head	*t_buffers;
>  
> @@ -631,7 +631,7 @@ struct transaction_s
>  	/*
>  	 * Doubly-linked circular list of metadata buffers being shadowed by log
>  	 * IO.  The IO buffers on the iobuf list and the shadow buffers on this
> -	 * list match each other one for one at all times. [j_list_lock]
> +	 * list match each other one for one at all times. [j_list_lock, no locks needed for jbd2 thread]
>  	 */
>  	struct journal_head	*t_shadow_list;
>  
> 

-- 
Technische Universität Dortmund
Alexander Lochmann                PGP key: 0xBC3EF6FD
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