Re: [PATCH 01/11] fs: provide unlocked helper for freeze_super()

[Jan Kara]

On Wed 29-11-17 15:23:46, Luis R. Rodriguez wrote:
> freeze_super() holds a write lock, however we wish to also enable
> callers which already hold the write lock. To do this provide a helper
> and make freeze_super() use it. This way, all that freeze_super() does
> now is lock handling and active count management.
> 
> This change has no functional changes.
> 
> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/super.c | 100 +++++++++++++++++++++++++++++++++----------------------------
>  1 file changed, 55 insertions(+), 45 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index d4e33e8f1e6f..a7650ff22f0e 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1387,59 +1387,20 @@ static void sb_freeze_unlock(struct super_block *sb)
>  		percpu_up_write(sb->s_writers.rw_sem + level);
>  }
>  
> -/**
> - * freeze_super - lock the filesystem and force it into a consistent state
> - * @sb: the super to lock
> - *
> - * Syncs the super to make sure the filesystem is consistent and calls the fs's
> - * freeze_fs.  Subsequent calls to this without first thawing the fs will return
> - * -EBUSY.
> - *
> - * During this function, sb->s_writers.frozen goes through these values:
> - *
> - * SB_UNFROZEN: File system is normal, all writes progress as usual.
> - *
> - * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
> - * writes should be blocked, though page faults are still allowed. We wait for
> - * all writes to complete and then proceed to the next stage.
> - *
> - * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
> - * but internal fs threads can still modify the filesystem (although they
> - * should not dirty new pages or inodes), writeback can run etc. After waiting
> - * for all running page faults we sync the filesystem which will clean all
> - * dirty pages and inodes (no new dirty pages or inodes can be created when
> - * sync is running).
> - *
> - * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
> - * modification are blocked (e.g. XFS preallocation truncation on inode
> - * reclaim). This is usually implemented by blocking new transactions for
> - * filesystems that have them and need this additional guard. After all
> - * internal writers are finished we call ->freeze_fs() to finish filesystem
> - * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
> - * mostly auxiliary for filesystems to verify they do not modify frozen fs.
> - *
> - * sb->s_writers.frozen is protected by sb->s_umount.
> - */
> -int freeze_super(struct super_block *sb)
> +/* Caller takes lock and handles active count */
> +static int freeze_locked_super(struct super_block *sb)
>  {
>  	int ret;
>  
> -	atomic_inc(&sb->s_active);
> -	down_write(&sb->s_umount);
> -	if (sb->s_writers.frozen != SB_UNFROZEN) {
> -		deactivate_locked_super(sb);
> +	if (sb->s_writers.frozen != SB_UNFROZEN)
>  		return -EBUSY;
> -	}
>  
> -	if (!(sb->s_flags & SB_BORN)) {
> -		up_write(&sb->s_umount);
> +	if (!(sb->s_flags & SB_BORN))
>  		return 0;	/* sic - it's "nothing to do" */
> -	}
>  
>  	if (sb_rdonly(sb)) {
>  		/* Nothing to do really... */
>  		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
> -		up_write(&sb->s_umount);
>  		return 0;
>  	}
>  
> @@ -1468,7 +1429,6 @@ int freeze_super(struct super_block *sb)
>  			sb->s_writers.frozen = SB_UNFROZEN;
>  			sb_freeze_unlock(sb);
>  			wake_up(&sb->s_writers.wait_unfrozen);
> -			deactivate_locked_super(sb);
>  			return ret;
>  		}
>  	}
> @@ -1478,9 +1438,59 @@ int freeze_super(struct super_block *sb)
>  	 */
>  	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
>  	lockdep_sb_freeze_release(sb);
> -	up_write(&sb->s_umount);
>  	return 0;
>  }
> +
> +/**
> + * freeze_super - lock the filesystem and force it into a consistent state
> + * @sb: the super to lock
> + *
> + * Syncs the super to make sure the filesystem is consistent and calls the fs's
> + * freeze_fs.  Subsequent calls to this without first thawing the fs will return
> + * -EBUSY.
> + *
> + * During this function, sb->s_writers.frozen goes through these values:
> + *
> + * SB_UNFROZEN: File system is normal, all writes progress as usual.
> + *
> + * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
> + * writes should be blocked, though page faults are still allowed. We wait for
> + * all writes to complete and then proceed to the next stage.
> + *
> + * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
> + * but internal fs threads can still modify the filesystem (although they
> + * should not dirty new pages or inodes), writeback can run etc. After waiting
> + * for all running page faults we sync the filesystem which will clean all
> + * dirty pages and inodes (no new dirty pages or inodes can be created when
> + * sync is running).
> + *
> + * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
> + * modification are blocked (e.g. XFS preallocation truncation on inode
> + * reclaim). This is usually implemented by blocking new transactions for
> + * filesystems that have them and need this additional guard. After all
> + * internal writers are finished we call ->freeze_fs() to finish filesystem
> + * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
> + * mostly auxiliary for filesystems to verify they do not modify frozen fs.
> + *
> + * sb->s_writers.frozen is protected by sb->s_umount.
> + */
> +int freeze_super(struct super_block *sb)
> +{
> +	int error;
> +
> +	atomic_inc(&sb->s_active);
> +
> +	down_write(&sb->s_umount);
> +	error = freeze_locked_super(sb);
> +	if (error) {
> +		deactivate_locked_super(sb);
> +		goto out;
> +	}
> +	up_write(&sb->s_umount);
> +
> +out:
> +	return error;
> +}
>  EXPORT_SYMBOL(freeze_super);
>  
>  /**
> -- 
> 2.15.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR