Re: [PATCH 02/22] xfs: prepare for moving perag definitions and support to libxfs

[Brian Foster <bfoster@redhat.com>]

On Thu, May 06, 2021 at 05:20:34PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> The perag structures really need to be defined with the rest of the
> AG support infrastructure. The struct xfs_perag and init/teardown
> has been placed in xfs_mount.[ch] because there are differences in
> the structure between kernel and userspace. Mainly that userspace
> doesn't have a lot of the internal stuff that the kernel has for
> caches and discard and other such structures.
> 
> However, it makes more sense to move this to libxfs than to keep
> this separation because we are now moving to use struct perags
> everywhere in the code instead of passing raw agnumber_t values
> about. Hence we shoudl really move the support infrastructure to
> libxfs/xfs_ag.[ch].
> 
> To do this without breaking userspace, first we need to rearrange
> the structures and code so that all the kernel specific code is
> located together. This makes it simple for userspace to ifdef out
> the all the parts it does not need, minimising the code differences
> between kernel and userspace. The next commit will do the move...
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_mount.c | 50 ++++++++++++++++++++++++++--------------------
>  fs/xfs/xfs_mount.h | 19 +++++++++---------
>  2 files changed, 38 insertions(+), 31 deletions(-)
> 
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index 21c630dde476..2e6d42014346 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
...
> @@ -229,13 +220,27 @@ xfs_initialize_perag(
>  		}
>  		spin_unlock(&mp->m_perag_lock);
>  		radix_tree_preload_end();
> -		/* first new pag is fully initialized */
> -		if (first_initialised == NULLAGNUMBER)
> -			first_initialised = index;
> +
> +		spin_lock_init(&pag->pag_ici_lock);
> +		spin_lock_init(&pag->pagb_lock);
> +		spin_lock_init(&pag->pag_state_lock);
> +		INIT_DELAYED_WORK(&pag->pag_blockgc_work, xfs_blockgc_worker);
> +		INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC);
> +		init_waitqueue_head(&pag->pagb_wait);
> +		pag->pagb_count = 0;
> +		pag->pagb_tree = RB_ROOT;
> +
> +		error = xfs_buf_hash_init(pag);
> +		if (error)
> +			goto out_free_pag;
> +

There's error handling code earlier up in this function that still lands
in out_hash_destroy, which is now before we get to the _hash_init()
call.

>  		error = xfs_iunlink_init(pag);
>  		if (error)
>  			goto out_hash_destroy;
> -		spin_lock_init(&pag->pag_state_lock);
> +
> +		/* first new pag is fully initialized */
> +		if (first_initialised == NULLAGNUMBER)
> +			first_initialised = index;
>  	}
>  
>  	index = xfs_set_inode_alloc(mp, agcount);
> @@ -249,6 +254,7 @@ xfs_initialize_perag(
>  out_hash_destroy:
>  	xfs_buf_hash_destroy(pag);
>  out_free_pag:
> +	pag = radix_tree_delete(&mp->m_perag_tree, index);

Now if we get here with an allocated pag that hasn't been inserted to
the tree, I suspect this call would assign pag = NULL..

Brian

>  	kmem_free(pag);
>  out_unwind_new_pags:
>  	/* unwind any prior newly initialized pags */
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index bb67274ee23f..6e534be5eea8 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -338,6 +338,16 @@ typedef struct xfs_perag {
>  	xfs_agino_t	pagl_leftrec;
>  	xfs_agino_t	pagl_rightrec;
>  
> +	int		pagb_count;	/* pagb slots in use */
> +	uint8_t		pagf_refcount_level; /* recount btree height */
> +
> +	/* Blocks reserved for all kinds of metadata. */
> +	struct xfs_ag_resv	pag_meta_resv;
> +	/* Blocks reserved for the reverse mapping btree. */
> +	struct xfs_ag_resv	pag_rmapbt_resv;
> +
> +	/* -- kernel only structures below this line -- */
> +
>  	/*
>  	 * Bitsets of per-ag metadata that have been checked and/or are sick.
>  	 * Callers should hold pag_state_lock before accessing this field.
> @@ -364,19 +374,10 @@ typedef struct xfs_perag {
>  
>  	/* for rcu-safe freeing */
>  	struct rcu_head	rcu_head;
> -	int		pagb_count;	/* pagb slots in use */
> -
> -	/* Blocks reserved for all kinds of metadata. */
> -	struct xfs_ag_resv	pag_meta_resv;
> -	/* Blocks reserved for the reverse mapping btree. */
> -	struct xfs_ag_resv	pag_rmapbt_resv;
>  
>  	/* background prealloc block trimming */
>  	struct delayed_work	pag_blockgc_work;
>  
> -	/* reference count */
> -	uint8_t			pagf_refcount_level;
> -
>  	/*
>  	 * Unlinked inode information.  This incore information reflects
>  	 * data stored in the AGI, so callers must hold the AGI buffer lock
> -- 
> 2.31.1
>