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

[Badari Pulavarty]

On Fri, 2008-05-16 at 10:11 -0700, Mingming Cao wrote:
> On Fri, 2008-05-16 at 11:01 -0400, Josef Bacik wrote:
> 
> > 
> > Got a couple of whitespace problems above it looks like.  Thanks,
> > 
> 
> Thanks for catching this, below is updated patch, fixed the whitespace
> and comments.
> 
> 
> ---------------------------------------------------
> JBD: fix journal_try_to_free_buffers race with
> journal_commit_transaction
> 
> From: Mingming Cao <cmm@xxxxxxxxxx>
> 
> 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 specificly, 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,
> but 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 09:27:21.000000000
> -0700
> @@ -1648,12 +1648,49 @@ out:
>  	return;
>  }
> 
> +/*
> + * 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.
> + *
> + * Journal_try_to_free_buffers() will call this function to
> + * wait for the current transaction finishing syncing data buffers,
> before
> + * try to free that buffer.
> + *
> + * Called with journal->j_state_lock hold.

Fix wrapping lines ?

> + */
> +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;
> +}
> 
>  /**
>   * int journal_try_to_free_buffers() - try to free page buffers.
>   * @journal: journal for operation
>   * @page: to try and free
> - * @unused_gfp_mask: unused
> + * @gfp_mask: unused for allocation purpose. Here is used
> + * 	      as a flag to tell if direct IO is attemping to free buffers.
>   *
>   *
>   * For all the buffers on this page,
> @@ -1682,13 +1719,16 @@ out:
>   * journal_try_to_free_buffer() is changing its state.  But that
>   * cannot happen because we never reallocate freed data as metadata
>   * while the data is part of a transaction.  Yes?
> + *
> + * Return 0 on failure, 1 on success
>   */
>  int journal_try_to_free_buffers(journal_t *journal,
> -				struct page *page, gfp_t unused_gfp_mask)
> +				struct page *page, gfp_t gfp_mask)
>  {
>  	struct buffer_head *head;
>  	struct buffer_head *bh;
>  	int ret = 0;
> +	int dio = gfp_mask & __GFP_REPEAT;
> 
>  	J_ASSERT(PageLocked(page));
> 
> @@ -1713,7 +1753,31 @@ int journal_try_to_free_buffers(journal_
>  		if (buffer_jbd(bh))
>  			goto busy;
>  	} while ((bh = bh->b_this_page) != head);
> +
>  	ret = try_to_free_buffers(page);
> +
> + 	/*
> +	 * In the case of concurrent direct IO and buffered IO,
> +	 * There are a number of places where we
> +	 * could race with journal_commit_transaction(), the later still
> +	 * helds the reference to the buffers to free while processing them.
> +	 * try_to_free_buffers() failed to free those buffers,
> +	 * resulting in an unexpected EIO error
> +	 * returns back to the generic_file_direct_IO()
> +	 *
> +	 * So let's wait for the current transaction finished flush
> +	 * dirty data buffers before we try to free those buffers
> +	 * again. This wait is needed by direct IO code path only,
> +	 * gfp_mask __GFP_REPEAT is passed from the direct IO code
> +	 * path to flag if we need to wait and retry free buffers.
> +	 */
> +	if (ret == 0 && dio) {

drop "dio" variable and compare here, like 
	  if (ret == 0 && (gfp_mask & __GFP_REPEAT)

> +        	spin_lock(&journal->j_state_lock);
> +		journal_wait_for_transaction_sync_data(journal);
> +		ret = try_to_free_buffers(page);
> +		spin_unlock(&journal->j_state_lock);
> +	}

Thanks,
Badari

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