Re: [RFC PATCH 1/4] fs: introduce ->storage_lost() for memory-failure

[Darrick J. Wong]

On Tue, Sep 15, 2020 at 06:13:08PM +0800, Shiyang Ruan wrote:
> This function is used to handle errors which may cause data lost in
> filesystem.  Such as memory-failure in fsdax mode.
> 
> In XFS, it requires "rmapbt" feature in order to query for files or
> metadata which associated to the error block.  Then we could call fs
> recover functions to try to repair the damaged data.(did not implemented
> in this patch)
> 
> After that, the memory-failure also needs to kill processes who are
> using those files.  The struct mf_recover_controller is created to store
> necessary parameters.
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxxxxx>
> ---
>  fs/xfs/xfs_super.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |  1 +
>  include/linux/mm.h |  6 ++++
>  3 files changed, 87 insertions(+)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 71ac6c1cdc36..118d9c5d9e1e 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -35,6 +35,10 @@
>  #include "xfs_refcount_item.h"
>  #include "xfs_bmap_item.h"
>  #include "xfs_reflink.h"
> +#include "xfs_alloc.h"
> +#include "xfs_rmap.h"
> +#include "xfs_rmap_btree.h"
> +#include "xfs_bit.h"
>  
>  #include <linux/magic.h>
>  #include <linux/fs_context.h>
> @@ -1104,6 +1108,81 @@ xfs_fs_free_cached_objects(
>  	return xfs_reclaim_inodes_nr(XFS_M(sb), sc->nr_to_scan);
>  }
>  
> +static int
> +xfs_storage_lost_helper(
> +	struct xfs_btree_cur		*cur,
> +	struct xfs_rmap_irec		*rec,
> +	void				*priv)
> +{
> +	struct xfs_inode		*ip;
> +	struct mf_recover_controller	*mfrc = priv;
> +	int				rc = 0;
> +
> +	if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner)) {
> +		// TODO check and try to fix metadata
> +	} else {
> +		/*
> +		 * Get files that incore, filter out others that are not in use.
> +		 */
> +		xfs_iget(cur->bc_mp, cur->bc_tp, rec->rm_owner, XFS_IGET_INCORE,
> +			 0, &ip);

Missing return value check here.

> +		if (!ip)
> +			return 0;
> +		if (!VFS_I(ip)->i_mapping)
> +			goto out;
> +
> +		rc = mfrc->recover_fn(mfrc->pfn, mfrc->flags,
> +				      VFS_I(ip)->i_mapping, rec->rm_offset);
> +
> +		// TODO try to fix data
> +out:
> +		xfs_irele(ip);
> +	}
> +
> +	return rc;
> +}
> +
> +static int
> +xfs_fs_storage_lost(
> +	struct super_block	*sb,
> +	loff_t			offset,

offset into which device?  XFS supports three...

I'm also a little surprised you don't pass in a length.

I guess that means this function will get called repeatedly for every
byte in the poisoned range?

> +	void			*priv)
> +{
> +	struct xfs_mount	*mp = XFS_M(sb);
> +	struct xfs_trans	*tp = NULL;
> +	struct xfs_btree_cur	*cur = NULL;
> +	struct xfs_rmap_irec	rmap_low, rmap_high;
> +	struct xfs_buf		*agf_bp = NULL;
> +	xfs_fsblock_t		fsbno = XFS_B_TO_FSB(mp, offset);
> +	xfs_agnumber_t		agno = XFS_FSB_TO_AGNO(mp, fsbno);
> +	xfs_agblock_t		agbno = XFS_FSB_TO_AGBNO(mp, fsbno);
> +	int			error = 0;
> +
> +	error = xfs_trans_alloc_empty(mp, &tp);
> +	if (error)
> +		return error;
> +
> +	error = xfs_alloc_read_agf(mp, tp, agno, 0, &agf_bp);
> +	if (error)
> +		return error;
> +
> +	cur = xfs_rmapbt_init_cursor(mp, tp, agf_bp, agno);

...and this is definitely the wrong call sequence if the malfunctioning
device is the realtime device.  If a dax rt device dies, you'll be
shooting down files on the data device, which will cause all sorts of
problems.

Question: Should all this poison recovery stuff go into a new file?
xfs_poison.c?  There's already a lot of code in xfs_super.c.

--D

> +
> +	/* Construct a range for rmap query */
> +	memset(&rmap_low, 0, sizeof(rmap_low));
> +	memset(&rmap_high, 0xFF, sizeof(rmap_high));
> +	rmap_low.rm_startblock = rmap_high.rm_startblock = agbno;
> +
> +	error = xfs_rmap_query_range(cur, &rmap_low, &rmap_high,
> +				     xfs_storage_lost_helper, priv);
> +	if (error == -ECANCELED)
> +		error = 0;
> +
> +	xfs_btree_del_cursor(cur, error);
> +	xfs_trans_brelse(tp, agf_bp);
> +	return error;
> +}
> +
>  static const struct super_operations xfs_super_operations = {
>  	.alloc_inode		= xfs_fs_alloc_inode,
>  	.destroy_inode		= xfs_fs_destroy_inode,
> @@ -1117,6 +1196,7 @@ static const struct super_operations xfs_super_operations = {
>  	.show_options		= xfs_fs_show_options,
>  	.nr_cached_objects	= xfs_fs_nr_cached_objects,
>  	.free_cached_objects	= xfs_fs_free_cached_objects,
> +	.storage_lost		= xfs_fs_storage_lost,
>  };
>  
>  static int
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e019ea2f1347..bd90485cfdc9 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1951,6 +1951,7 @@ struct super_operations {
>  				  struct shrink_control *);
>  	long (*free_cached_objects)(struct super_block *,
>  				    struct shrink_control *);
> +	int (*storage_lost)(struct super_block *sb, loff_t offset, void *priv);
>  };
>  
>  /*
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 1983e08f5906..3f0c36e1bf3d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3002,6 +3002,12 @@ extern void shake_page(struct page *p, int access);
>  extern atomic_long_t num_poisoned_pages __read_mostly;
>  extern int soft_offline_page(unsigned long pfn, int flags);
>  
> +struct mf_recover_controller {
> +	int (*recover_fn)(unsigned long pfn, int flags,
> +		struct address_space *mapping, pgoff_t index);
> +	unsigned long pfn;
> +	int flags;
> +};
>  
>  /*
>   * Error handlers for various types of pages.
> -- 
> 2.28.0
> 
> 
>