Re: [PATCH] md: don't return -EAGAIN in md_allow_write for external metadata arrays

[Shaohua Li <shli@kernel.org>]

On Mon, May 08, 2017 at 11:56:55AM +0200, Artur Paszkiewicz wrote:
> This essentially reverts commit b5470dc5fc18 ("md: resolve external
> metadata handling deadlock in md_allow_write") with some adjustments.
> 
> Since commit 6791875e2e53 ("md: make reconfig_mutex optional for writes
> to md sysfs files.") changing array_state to 'active' does not use
> mddev_lock() and will not cause a deadlock with md_allow_write(). This
> revert simplifies userspace tools that write to sysfs attributes like
> "stripe_cache_size" or "consistency_policy" because it removes the need
> for special handling for external metadata arrays, checking for EAGAIN
> and retrying the write.

applied, thanks!
 
> Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
> ---
>  drivers/md/md.c    | 20 ++++++++------------
>  drivers/md/md.h    |  2 +-
>  drivers/md/raid1.c |  9 +++------
>  drivers/md/raid5.c | 12 +++---------
>  4 files changed, 15 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 82f798be964f..10367ffe92e3 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8022,18 +8022,15 @@ EXPORT_SYMBOL(md_write_end);
>   * may proceed without blocking.  It is important to call this before
>   * attempting a GFP_KERNEL allocation while holding the mddev lock.
>   * Must be called with mddev_lock held.
> - *
> - * In the ->external case MD_SB_CHANGE_PENDING can not be cleared until mddev->lock
> - * is dropped, so return -EAGAIN after notifying userspace.
>   */
> -int md_allow_write(struct mddev *mddev)
> +void md_allow_write(struct mddev *mddev)
>  {
>  	if (!mddev->pers)
> -		return 0;
> +		return;
>  	if (mddev->ro)
> -		return 0;
> +		return;
>  	if (!mddev->pers->sync_request)
> -		return 0;
> +		return;
>  
>  	spin_lock(&mddev->lock);
>  	if (mddev->in_sync) {
> @@ -8046,13 +8043,12 @@ int md_allow_write(struct mddev *mddev)
>  		spin_unlock(&mddev->lock);
>  		md_update_sb(mddev, 0);
>  		sysfs_notify_dirent_safe(mddev->sysfs_state);
> +		/* wait for the dirty state to be recorded in the metadata */
> +		wait_event(mddev->sb_wait,
> +			   !test_bit(MD_SB_CHANGE_CLEAN, &mddev->sb_flags) &&
> +			   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags));
>  	} else
>  		spin_unlock(&mddev->lock);
> -
> -	if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags))
> -		return -EAGAIN;
> -	else
> -		return 0;
>  }
>  EXPORT_SYMBOL_GPL(md_allow_write);
>  
> diff --git a/drivers/md/md.h b/drivers/md/md.h
> index 4e75d121bfcc..11f15146ce51 100644
> --- a/drivers/md/md.h
> +++ b/drivers/md/md.h
> @@ -665,7 +665,7 @@ extern int sync_page_io(struct md_rdev *rdev, sector_t sector, int size,
>  			bool metadata_op);
>  extern void md_do_sync(struct md_thread *thread);
>  extern void md_new_event(struct mddev *mddev);
> -extern int md_allow_write(struct mddev *mddev);
> +extern void md_allow_write(struct mddev *mddev);
>  extern void md_wait_for_blocked_rdev(struct md_rdev *rdev, struct mddev *mddev);
>  extern void md_set_array_sectors(struct mddev *mddev, sector_t array_sectors);
>  extern int md_check_no_bitmap(struct mddev *mddev);
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 7ed59351fe97..7c1f73398800 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -3197,7 +3197,7 @@ static int raid1_reshape(struct mddev *mddev)
>  	struct r1conf *conf = mddev->private;
>  	int cnt, raid_disks;
>  	unsigned long flags;
> -	int d, d2, err;
> +	int d, d2;
>  
>  	/* Cannot change chunk_size, layout, or level */
>  	if (mddev->chunk_sectors != mddev->new_chunk_sectors ||
> @@ -3209,11 +3209,8 @@ static int raid1_reshape(struct mddev *mddev)
>  		return -EINVAL;
>  	}
>  
> -	if (!mddev_is_clustered(mddev)) {
> -		err = md_allow_write(mddev);
> -		if (err)
> -			return err;
> -	}
> +	if (!mddev_is_clustered(mddev))
> +		md_allow_write(mddev);
>  
>  	raid_disks = mddev->raid_disks + mddev->delta_disks;
>  
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 3809a2192132..f8055a7abb4b 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -2309,14 +2309,12 @@ static int resize_stripes(struct r5conf *conf, int newsize)
>  	struct stripe_head *osh, *nsh;
>  	LIST_HEAD(newstripes);
>  	struct disk_info *ndisks;
> -	int err;
> +	int err = 0;
>  	struct kmem_cache *sc;
>  	int i;
>  	int hash, cnt;
>  
> -	err = md_allow_write(conf->mddev);
> -	if (err)
> -		return err;
> +	md_allow_write(conf->mddev);
>  
>  	/* Step 1 */
>  	sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
> @@ -6310,7 +6308,6 @@ int
>  raid5_set_cache_size(struct mddev *mddev, int size)
>  {
>  	struct r5conf *conf = mddev->private;
> -	int err;
>  
>  	if (size <= 16 || size > 32768)
>  		return -EINVAL;
> @@ -6322,10 +6319,7 @@ raid5_set_cache_size(struct mddev *mddev, int size)
>  		;
>  	mutex_unlock(&conf->cache_size_mutex);
>  
> -
> -	err = md_allow_write(mddev);
> -	if (err)
> -		return err;
> +	md_allow_write(mddev);
>  
>  	mutex_lock(&conf->cache_size_mutex);
>  	while (size > conf->max_nr_stripes)
> -- 
> 2.11.0
> 
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