linux-ext4 - Re: [PATCH 15/22] jbd2: Factor out common parts of stopping and restarting a handle

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Date:   Mon, 21 Oct 2019 13:49:33 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH 15/22] jbd2: Factor out common parts of stopping and
 restarting a handle

On Fri, Oct 04, 2019 at 12:06:01AM +0200, Jan Kara wrote:
> jbd2__journal_restart() has quite some code that is common with
> jbd2_journal_stop(). Factor this functionality into stop_this_handle()
> helper and use it from both functions. Note that this also drops
> t_handle_lock protection from jbd2__journal_restart() as
> jbd2_journal_stop() does the same thing without it.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
>  fs/jbd2/transaction.c | 94 +++++++++++++++++++++++----------------------------
>  1 file changed, 42 insertions(+), 52 deletions(-)
> 
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index d648cec3f90f..d4ee02e5161b 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -677,52 +704,30 @@ int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask)

> -	read_lock(&journal->j_state_lock);
> -	spin_lock(&transaction->t_handle_lock);
> -	atomic_sub(handle->h_buffer_credits,
> -		   &transaction->t_outstanding_credits);
> -	if (handle->h_rsv_handle) {
> -		sub_reserved_credits(journal,
> -				     handle->h_rsv_handle->h_buffer_credits);
> -	}
> -	if (atomic_dec_and_test(&transaction->t_updates))
> -		wake_up(&journal->j_wait_updates);
> -	tid = transaction->t_tid;
> -	spin_unlock(&transaction->t_handle_lock);
> +	jbd_debug(2, "restarting handle %p\n", handle);
> +	stop_this_handle(handle);
>  	handle->h_transaction = NULL;
> -	current->journal_info = NULL;
>  
> -	jbd_debug(2, "restarting handle %p\n", handle);
> +	read_lock(&journal->j_state_lock);
>  	need_to_start = !tid_geq(journal->j_commit_request, tid);
>  	read_unlock(&journal->j_state_lock);

What is j_state_lock protecting at this point?  There's only a 32-bit
read of j_commit_request at this point.

						- Ted