Re: [PATCH] Fix DIO EIO error caused by race betweenjbd_commit_transaction() and journal_try_to_drop_buffers()

[Josef Bacik]

On Fri, May 16, 2008 at 07:14:10AM -0700, Mingming Cao wrote:
> This patch fixed a few races between direct IO and kjournld commit transaction.
> An unexpected EIO error gets returned to direct IO caller when it failed to
> free those data buffers. This could be reproduced easily with parallel 
> direct write and buffered write to the same file
> 
> More specific, those races could cause journal_try_to_free_buffers()
> fail to free the data buffers, when jbd is committing the transaction that has
> those data buffers on its t_syncdata_list or t_locked_list. 
> journal_commit_transaction() still holds the reference to those buffers
>  before data reach to disk and buffers are removed from the 
> t_syncdata_list of t_locked_list. This prevent the concurrent 
> journal_try_to_free_buffers() to free those buffers at the same time, and cause
> EIO error returns back to direct IO.
> 
> With this patch, in case of direct IO and when try_to_free_buffers() failed,
> let's waiting for journal_commit_transaction() to finish
> flushing the current committing transaction's data buffers to disk, 
> then try to free those buffers again.
> 
> Signed-off-by: Mingming Cao <cmm@xxxxxxxxxx>
> Reviewed-by: Badari Pulavarty <pbadari@xxxxxxxxxx> 
> ---
>  fs/jbd/commit.c      |    1 +
>  fs/jbd/journal.c     |    1 +
>  fs/jbd/transaction.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/jbd.h  |    3 +++
>  4 files changed, 51 insertions(+)
> 
> Index: linux-2.6.26-rc1/include/linux/jbd.h
> ===================================================================
> --- linux-2.6.26-rc1.orig/include/linux/jbd.h	2008-05-14 16:36:41.000000000 -0700
> +++ linux-2.6.26-rc1/include/linux/jbd.h	2008-05-15 14:12:10.000000000 -0700
> @@ -667,6 +667,9 @@ struct journal_s
>  	 */
>  	wait_queue_head_t	j_wait_transaction_locked;
>  
> +	/* Wait queu for waiting for data buffers to flushed to disk*/
> +	wait_queue_head_t	j_wait_data_flushed;
> +
>  	/* Wait queue for waiting for checkpointing to complete */
>  	wait_queue_head_t	j_wait_logspace;
>  
> Index: linux-2.6.26-rc1/fs/jbd/commit.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/fs/jbd/commit.c	2008-05-03 11:59:44.000000000 -0700
> +++ linux-2.6.26-rc1/fs/jbd/commit.c	2008-05-15 14:12:46.000000000 -0700
> @@ -462,6 +462,7 @@ void journal_commit_transaction(journal_
>  	 * clean by now, so check that it is in fact empty.
>  	 */
>  	J_ASSERT (commit_transaction->t_sync_datalist == NULL);
> +	wake_up(&journal->j_wait_data_flushed)
>  
>  	jbd_debug (3, "JBD: commit phase 3\n");
>  
> Index: linux-2.6.26-rc1/fs/jbd/journal.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/fs/jbd/journal.c	2008-05-14 16:36:41.000000000 -0700
> +++ linux-2.6.26-rc1/fs/jbd/journal.c	2008-05-15 14:13:02.000000000 -0700
> @@ -660,6 +660,7 @@ static journal_t * journal_init_common (
>  		goto fail;
>  
>  	init_waitqueue_head(&journal->j_wait_transaction_locked);
> +	init_waitqueue_head(&journal->j_wait_data_flushed);
>  	init_waitqueue_head(&journal->j_wait_logspace);
>  	init_waitqueue_head(&journal->j_wait_done_commit);
>  	init_waitqueue_head(&journal->j_wait_checkpoint);
> Index: linux-2.6.26-rc1/fs/jbd/transaction.c
> ===================================================================
> --- linux-2.6.26-rc1.orig/fs/jbd/transaction.c	2008-05-03 11:59:44.000000000 -0700
> +++ linux-2.6.26-rc1/fs/jbd/transaction.c	2008-05-16 06:42:30.000000000 -0700
> @@ -1648,12 +1648,47 @@ out:
>  	return;
>  }
>  
> +/*
> + * Journal_try_to_free_buffers() will call this function to w
> + * waiting for the current transaction finishing syncing data buffers, before
> + * try to free that buffer.
> + *
> + * journal_try_to_free_buffers() could race with journal_commit_transaction()
> + * The later might still hold the reference count to the buffers when inspecting
> + * them on t_syncdata_list or t_locked_list.
> + */
> +static void journal_wait_for_transaction_sync_data(journal_t *journal)
> +{
> +        transaction_t *transaction = NULL;
> +
> +        transaction = journal->j_committing_transaction;
> +
> +        if (!transaction)
> +                return;
> +
> +        /*
> +         * If the current transaction is flushing and waiting for data buffers
> +	 * (t_state is T_FLUSH), wait for the j_wait_data_flushed event
> +         */
> +        if (transaction->t_state == T_FLUSH) {
> +                DEFINE_WAIT(wait);
> +
> +                prepare_to_wait(&journal->j_wait_data_flushed,
> +                                        &wait, TASK_UNINTERRUPTIBLE);
> +                spin_unlock(&journal->j_state_lock);
> +                schedule();
> +                finish_wait(&journal->j_wait_data_flushed, &wait);
> +        	spin_lock(&journal->j_state_lock);
> +        }
> +	return;
> +}
> 

Got a couple of whitespace problems above it looks like.  Thanks,

Josef

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