Re: [PATCH 06/11] ext4: serialize dio nonlocked reads with defrag workers V3

[Jan Kara <jack@suse.cz>]

On Fri 28-09-12 19:44:06, Dmitry Monakhov wrote:
> Inode's block defrag and ext4_change_inode_journal_flag() may
> affect nonlocked DIO reads result, so proper synchronization
> required.
> 
> - Add missed inode_dio_wait() calls where appropriate
> - Check inode state under extra i_dio_count reference.
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Changes from V2:
> - fix mistype in condition
> Changes from V1:
> - add missed memory bariers
> - move DIOREAD_LOCK state check out from generic should_dioread_nolock
>   otherwise it will affect existing DIO readers.
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
> ---
>  fs/ext4/ext4.h        |   17 +++++++++++++++++
>  fs/ext4/indirect.c    |   14 ++++++++++++++
>  fs/ext4/inode.c       |    5 +++++
>  fs/ext4/move_extent.c |    8 ++++++++
>  4 files changed, 44 insertions(+), 0 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 9c3d004..885dc79 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1363,6 +1363,8 @@ enum {
>  	EXT4_STATE_DIO_UNWRITTEN,	/* need convert on dio done*/
>  	EXT4_STATE_NEWENTRY,		/* File just added to dir */
>  	EXT4_STATE_DELALLOC_RESERVED,	/* blks already reserved for delalloc */
> +	EXT4_STATE_DIOREAD_LOCK,	/* Disable support for dio read
> +					   nolocking */
>  };
>  
>  #define EXT4_INODE_BIT_FNS(name, field, offset)				\
> @@ -2471,6 +2473,21 @@ static inline void set_bitmap_uptodate(struct buffer_head *bh)
>  	set_bit(BH_BITMAP_UPTODATE, &(bh)->b_state);
>  }
>  
> +/*
> + * Disable DIO read nolock optimization, so new dioreaders will be forced
> + * to grab i_mutex
> + */
> +static inline void ext4_inode_block_unlocked_dio(struct inode *inode)
> +{
> +	ext4_set_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
> +	smp_mb();
> +}
> +static inline void ext4_inode_resume_unlocked_dio(struct inode *inode)
> +{
> +	smp_mb();
> +	ext4_clear_inode_state(inode, EXT4_STATE_DIOREAD_LOCK);
> +}
> +
>  #define in_range(b, first, len)	((b) >= (first) && (b) <= (first) + (len) - 1)
>  
>  /* For ioend & aio unwritten conversion wait queues */
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index ebc7d83..9e6cdb6 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -811,11 +811,25 @@ retry:
>  		if (unlikely(!list_empty(&ei->i_completed_io_list)))
>  			ext4_flush_completed_IO(inode);
>  
> +		/*
> +		 * Nolock dioread optimization may be dynamically disabled
> +		 * via ext4_inode_block_unlocked_dio(). Check inode's state
> +		 * while holding extra i_dio_count ref.
> +		 */
> +		atomic_inc(&inode->i_dio_count);
> +		smp_mb();
> +		if (unlikely(ext4_test_inode_state(inode,
> +						    EXT4_STATE_DIOREAD_LOCK))) {
> +			inode_dio_done(inode);
> +			goto locked;
> +		}
>  		ret = __blockdev_direct_IO(rw, iocb, inode,
>  				 inode->i_sb->s_bdev, iov,
>  				 offset, nr_segs,
>  				 ext4_get_block, NULL, NULL, 0);
> +		inode_dio_done(inode);
>  	} else {
> +locked:
>  		ret = blockdev_direct_IO(rw, iocb, inode, iov,
>  				 offset, nr_segs, ext4_get_block);
>  
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 1ea34e5..da52855 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4692,6 +4692,10 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
>  			return err;
>  	}
>  
> +	/* Wait for all existing dio workers */
> +	ext4_inode_block_unlocked_dio(inode);
> +	inode_dio_wait(inode);
> +
>  	jbd2_journal_lock_updates(journal);
>  
>  	/*
> @@ -4711,6 +4715,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
>  	ext4_set_aops(inode);
>  
>  	jbd2_journal_unlock_updates(journal);
> +	ext4_inode_resume_unlocked_dio(inode);
>  
>  	/* Finally we can mark the inode as dirty. */
>  
> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> index c2e47da..0aaaf12 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -1325,6 +1325,12 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp,
>  	/* Protect orig and donor inodes against a truncate */
>  	mext_inode_double_lock(orig_inode, donor_inode);
>  
> +	/* Wait for all existing dio workers */
> +	ext4_inode_block_unlocked_dio(orig_inode);
> +	ext4_inode_block_unlocked_dio(donor_inode);
> +	inode_dio_wait(orig_inode);
> +	inode_dio_wait(donor_inode);
> +
>  	/* Protect extent tree against block allocations via delalloc */
>  	double_down_write_data_sem(orig_inode, donor_inode);
>  	/* Check the filesystem environment whether move_extent can be done */
> @@ -1523,6 +1529,8 @@ out:
>  		kfree(holecheck_path);
>  	}
>  	double_up_write_data_sem(orig_inode, donor_inode);
> +	ext4_inode_resume_unlocked_dio(orig_inode);
> +	ext4_inode_resume_unlocked_dio(donor_inode);
>  	mext_inode_double_unlock(orig_inode, donor_inode);
>  
>  	return ret;
> -- 
> 1.7.7.6
>