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Date:	Mon, 5 Mar 2012 11:09:33 +0100
From:	Jan Kara <jack@...e.cz>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, jack@...e.cz, hch@...radead.org
Subject: Re: [PATCH 6/7] ext4: honor the O_SYNC flag for aysnchronous
 direct I/O requests

On Fri 02-03-12 14:56:14, Jeff Moyer wrote:
> Hi,
> 
> If a file is opened with O_SYNC|O_DIRECT, the drive cache does not get
> flushed after the write completion.  Instead, it's flushed *before* the
> I/O is sent to the disk (in __generic_file_aio_write).  This patch
> attempts to fix that problem by marking an I/O as requiring a cache
> flush in endio processing.  I'll send a follow-on patch to the
> generic write code to get rid of the bogus generic_write_sync call
> when EIOCBQUEUED is returned.
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
> 
> Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
> ---
>  fs/ext4/ext4.h    |    4 +++
>  fs/ext4/inode.c   |   11 ++++++-
>  fs/ext4/page-io.c |   73 +++++++++++++++++++++++++++++++++++++++++++++++-----
>  fs/ext4/super.c   |   11 ++++++++
>  4 files changed, 90 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 3ce6a0c..e1478be 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -186,6 +186,7 @@ struct mpage_da_data {
>  #define EXT4_IO_END_QUEUED	0x0004
>  #define EXT4_IO_END_DIRECT	0x0008
>  #define EXT4_IO_END_IN_FSYNC	0x0010
> +#define EXT4_IO_END_NEEDS_SYNC	0x0020
>  
>  struct ext4_io_page {
>  	struct page	*p_page;
> @@ -1248,6 +1249,9 @@ struct ext4_sb_info {
>  	/* workqueue for dio unwritten */
>  	struct workqueue_struct *dio_unwritten_wq;
>  
> +	/* workqueue for aio+dio+o_sync disk cache flushing */
> +	struct workqueue_struct *aio_dio_flush_wq;
> +
>  	/* timer for periodic error stats printing */
>  	struct timer_list s_err_report;
>  
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index f6dc02b..13cdb4c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2769,8 +2769,12 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
>  
>  	iocb->private = NULL;
>  
> +	/* AIO+DIO+O_SYNC I/Os need a cache flush after completion */
> +	if (is_async && (IS_SYNC(inode) || (iocb->ki_filp->f_flags & O_DSYNC)))
> +		io_end->flag |= EXT4_IO_END_NEEDS_SYNC;
> +
>  	/* if not aio dio with unwritten extents, just free io and return */
> -	if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
> +	if (!(io_end->flag & (EXT4_IO_END_UNWRITTEN|EXT4_IO_END_NEEDS_SYNC))) {
>  		ext4_free_io_end(io_end);
>  out:
>  		if (is_async)
> @@ -2785,7 +2789,10 @@ out:
>  		io_end->iocb = iocb;
>  		io_end->result = ret;
>  	}
> -	wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
> +	if (io_end->flag & EXT4_IO_END_UNWRITTEN)
> +		wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
> +	else
> +		wq = EXT4_SB(io_end->inode->i_sb)->aio_dio_flush_wq;
>  
>  	/* Add the io_end to per-inode completed aio dio list*/
>  	ei = EXT4_I(io_end->inode);
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index dcdeef1..baa1b84 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -82,6 +82,50 @@ void ext4_free_io_end(ext4_io_end_t *io)
>  }
>  
>  /*
> + * This function is called in the completion path for AIO O_SYNC|O_DIRECT
> + * writes, and also in the fsync path.  The purpose is to ensure that the
> + * disk caches for the journal and data devices are flushed.
> + */
> +static int ext4_end_io_do_flush(ext4_io_end_t *io)
> +{
> +	struct inode *inode = io->inode;
> +	tid_t commit_tid;
> +	bool needs_barrier = false;
> +	journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
> +	int barriers_enabled = test_opt(inode->i_sb, BARRIER);
> +	int ret = 0;
> +
> +	if (!barriers_enabled)
> +		return 0;
> +
> +	/*
> +	 * If we are running in nojournal mode, just flush the disk
> +	 * cache and return.
> +	 */
> +	if (!journal)
> +		return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL);
> +
> +	if (ext4_should_journal_data(inode)) {
> +		ret = ext4_force_commit(inode->i_sb);
> +		goto out;
> +	}
> +
> +	commit_tid = io->iocb->ki_filp->f_flags & __O_SYNC ?
> +		EXT4_I(inode)->i_sync_tid : EXT4_I(inode)->i_datasync_tid;
> +	if (!jbd2_trans_will_send_data_barrier(journal, commit_tid))
> +		needs_barrier = true;
> +
> +	jbd2_log_start_commit(journal, commit_tid);
> +	ret = jbd2_log_wait_commit(journal, commit_tid);
> +
> +	if (!ret && needs_barrier)
> +		ret = blkdev_issue_flush(inode->i_sb->s_bdev, GFP_NOIO, NULL);
> +
> +out:
> +	return ret;
> +}
> +
> +/*
>   * check a range of space and convert unwritten extents to written.
>   *
>   * Called with inode->i_mutex; we depend on this when we manipulate
> @@ -98,15 +142,30 @@ int ext4_end_io_nolock(ext4_io_end_t *io)
>  		   "list->prev 0x%p\n",
>  		   io, inode->i_ino, io->list.next, io->list.prev);
>  
> -	ret = ext4_convert_unwritten_extents(inode, offset, size);
> -	if (ret < 0) {
> -		ext4_msg(inode->i_sb, KERN_EMERG,
> -			 "failed to convert unwritten extents to written "
> -			 "extents -- potential data loss!  "
> -			 "(inode %lu, offset %llu, size %zd, error %d)",
> -			 inode->i_ino, offset, size, ret);
> +	if (io->flag & EXT4_IO_END_UNWRITTEN) {
> +
> +		ret = ext4_convert_unwritten_extents(inode, offset, size);
> +		if (ret < 0) {
> +			ext4_msg(inode->i_sb, KERN_EMERG,
> +				 "failed to convert unwritten extents to "
> +				 "written extents -- potential data loss!  "
> +				 "(inode %lu, offset %llu, size %zd, error %d)",
> +				 inode->i_ino, offset, size, ret);
> +			goto endio;
> +		}
>  	}
>  
> +	/*
> +	 * This function has two callers.  The first is the end_io_work
> +	 * routine just below, which is an asynchronous completion context.
> +	 * The second is in the fsync path.  For the latter path, we can't
> +	 * return from here until the job is done.  Hence,
> +	 * ext4_end_io_do_flush is blocking.
> +	 */
> +	if (io->flag & EXT4_IO_END_NEEDS_SYNC)
> +		ret = ext4_end_io_do_flush(io);
> +
> +endio:
>  	if (io->iocb)
>  		aio_complete(io->iocb, io->result, 0);
>  
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 502c61f..a24938e 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -805,6 +805,7 @@ static void ext4_put_super(struct super_block *sb)
>  	dquot_disable(sb, -1, DQUOT_USAGE_ENABLED | DQUOT_LIMITS_ENABLED);
>  
>  	flush_workqueue(sbi->dio_unwritten_wq);
> +	destroy_workqueue(sbi->aio_dio_flush_wq);
>  	destroy_workqueue(sbi->dio_unwritten_wq);
>  
>  	lock_super(sb);
> @@ -3718,6 +3719,13 @@ no_journal:
>  		goto failed_mount_wq;
>  	}
>  
> +	EXT4_SB(sb)->aio_dio_flush_wq =
> +		alloc_workqueue("ext4-aio-dio-flush", WQ_MEM_RECLAIM | WQ_UNBOUND, 1);
> +	if (!EXT4_SB(sb)->aio_dio_flush_wq) {
> +		printk(KERN_ERR "EXT4-fs: failed to create flush workqueue\n");
> +		goto failed_flush_wq;
> +	}
> +
>  	/*
>  	 * The jbd2_journal_load will have done any necessary log recovery,
>  	 * so we can safely mount the rest of the filesystem now.
> @@ -3840,6 +3848,8 @@ failed_mount4a:
>  	sb->s_root = NULL;
>  failed_mount4:
>  	ext4_msg(sb, KERN_ERR, "mount failed");
> +	destroy_workqueue(EXT4_SB(sb)->aio_dio_flush_wq);
> +failed_flush_wq:
>  	destroy_workqueue(EXT4_SB(sb)->dio_unwritten_wq);
>  failed_mount_wq:
>  	if (sbi->s_journal) {
> @@ -4303,6 +4313,7 @@ static int ext4_sync_fs(struct super_block *sb, int wait)
>  
>  	trace_ext4_sync_fs(sb, wait);
>  	flush_workqueue(sbi->dio_unwritten_wq);
> +	flush_workqueue(sbi->aio_dio_flush_wq);
>  	if (jbd2_journal_start_commit(sbi->s_journal, &target)) {
>  		if (wait)
>  			jbd2_log_wait_commit(sbi->s_journal, target);
> -- 
> 1.7.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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