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Date: Thu, 2 Oct 2025 10:40:56 +0200
From: Jan Kara <jack@...e.cz>
To: Byungchul Park <byungchul@...com>
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Subject: Re: [PATCH v17 30/47] fs/jbd2: use a weaker annotation in journal
 handling

On Thu 02-10-25 17:12:30, Byungchul Park wrote:
> jbd2 journal handling code doesn't want jbd2_might_wait_for_commit()
> to be placed between start_this_handle() and stop_this_handle().  So it
> marks the region with rwsem_acquire_read() and rwsem_release().
> 
> However, the annotation is too strong for that purpose.  We don't have
> to use more than try lock annotation for that.
> 
> rwsem_acquire_read() implies:
> 
>    1. might be a waiter on contention of the lock.
>    2. enter to the critical section of the lock.
> 
> All we need in here is to act 2, not 1.  So trylock version of
> annotation is sufficient for that purpose.  Now that dept partially
> relies on lockdep annotaions, dept interpets rwsem_acquire_read() as a
> potential wait and might report a deadlock by the wait.
> 
> Replace it with trylock version of annotation.
> 
> Signed-off-by: Byungchul Park <byungchul@...com>

Indeed. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/jbd2/transaction.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index c7867139af69..b4e65f51bf5e 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -441,7 +441,7 @@ static int start_this_handle(journal_t *journal, handle_t *handle,
>  	read_unlock(&journal->j_state_lock);
>  	current->journal_info = handle;
>  
> -	rwsem_acquire_read(&journal->j_trans_commit_map, 0, 0, _THIS_IP_);
> +	rwsem_acquire_read(&journal->j_trans_commit_map, 0, 1, _THIS_IP_);
>  	jbd2_journal_free_transaction(new_transaction);
>  	/*
>  	 * Ensure that no allocations done while the transaction is open are
> -- 
> 2.17.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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