Re: [PATCH V11 10/14] xfs: Introduce error injection to reduce maximum inode fork extent count

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Nov 17, 2020 at 07:14:12PM +0530, Chandan Babu R wrote:
> This commit adds XFS_ERRTAG_REDUCE_MAX_IEXTENTS error tag which enables
> userspace programs to test "Inode fork extent count overflow detection"
> by reducing maximum possible inode fork extent count to 35.
> 
> With block size of 4k, xattr (with local value) insert operation would
> require in the worst case "XFS_DA_NODE_MAXDEPTH + 1" plus
> "XFS_DA_NODE_MAXDEPTH + (64k / 4k)" (required for guaranteeing removal
> of a maximum sized xattr) number of extents. This evaluates to ~28
> extents. To allow for additions of two or more xattrs during extent
> overflow testing, the pseudo max extent count is set to 35.
> 
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
>  fs/xfs/libxfs/xfs_errortag.h   | 4 +++-
>  fs/xfs/libxfs/xfs_inode_fork.c | 4 ++++
>  fs/xfs/xfs_error.c             | 3 +++
>  3 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_errortag.h b/fs/xfs/libxfs/xfs_errortag.h
> index 53b305dea381..1c56fcceeea6 100644
> --- a/fs/xfs/libxfs/xfs_errortag.h
> +++ b/fs/xfs/libxfs/xfs_errortag.h
> @@ -56,7 +56,8 @@
>  #define XFS_ERRTAG_FORCE_SUMMARY_RECALC			33
>  #define XFS_ERRTAG_IUNLINK_FALLBACK			34
>  #define XFS_ERRTAG_BUF_IOERROR				35
> -#define XFS_ERRTAG_MAX					36
> +#define XFS_ERRTAG_REDUCE_MAX_IEXTENTS			36
> +#define XFS_ERRTAG_MAX					37
>  
>  /*
>   * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
> @@ -97,5 +98,6 @@
>  #define XFS_RANDOM_FORCE_SUMMARY_RECALC			1
>  #define XFS_RANDOM_IUNLINK_FALLBACK			(XFS_RANDOM_DEFAULT/10)
>  #define XFS_RANDOM_BUF_IOERROR				XFS_RANDOM_DEFAULT
> +#define XFS_RANDOM_REDUCE_MAX_IEXTENTS			1
>  
>  #endif /* __XFS_ERRORTAG_H_ */
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.c b/fs/xfs/libxfs/xfs_inode_fork.c
> index 8d48716547e5..989b20977654 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.c
> +++ b/fs/xfs/libxfs/xfs_inode_fork.c
> @@ -24,6 +24,7 @@
>  #include "xfs_dir2_priv.h"
>  #include "xfs_attr_leaf.h"
>  #include "xfs_types.h"
> +#include "xfs_errortag.h"
>  
>  kmem_zone_t *xfs_ifork_zone;
>  
> @@ -745,6 +746,9 @@ xfs_iext_count_may_overflow(
>  
>  	max_exts = (whichfork == XFS_ATTR_FORK) ? MAXAEXTNUM : MAXEXTNUM;
>  
> +	if (XFS_TEST_ERROR(false, ip->i_mount, XFS_ERRTAG_REDUCE_MAX_IEXTENTS))
> +		max_exts = 35;

Please add a comment here explaining why 35.

Sorry about the longish review delay, last week was a US holiday and
this week I have eye problems again. :(

--D

> +
>  	nr_exts = ifp->if_nextents + nr_to_add;
>  	if (nr_exts < ifp->if_nextents || nr_exts > max_exts)
>  		return -EFBIG;
> diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
> index 7f6e20899473..3780b118cc47 100644
> --- a/fs/xfs/xfs_error.c
> +++ b/fs/xfs/xfs_error.c
> @@ -54,6 +54,7 @@ static unsigned int xfs_errortag_random_default[] = {
>  	XFS_RANDOM_FORCE_SUMMARY_RECALC,
>  	XFS_RANDOM_IUNLINK_FALLBACK,
>  	XFS_RANDOM_BUF_IOERROR,
> +	XFS_RANDOM_REDUCE_MAX_IEXTENTS,
>  };
>  
>  struct xfs_errortag_attr {
> @@ -164,6 +165,7 @@ XFS_ERRORTAG_ATTR_RW(force_repair,	XFS_ERRTAG_FORCE_SCRUB_REPAIR);
>  XFS_ERRORTAG_ATTR_RW(bad_summary,	XFS_ERRTAG_FORCE_SUMMARY_RECALC);
>  XFS_ERRORTAG_ATTR_RW(iunlink_fallback,	XFS_ERRTAG_IUNLINK_FALLBACK);
>  XFS_ERRORTAG_ATTR_RW(buf_ioerror,	XFS_ERRTAG_BUF_IOERROR);
> +XFS_ERRORTAG_ATTR_RW(reduce_max_iextents,	XFS_ERRTAG_REDUCE_MAX_IEXTENTS);
>  
>  static struct attribute *xfs_errortag_attrs[] = {
>  	XFS_ERRORTAG_ATTR_LIST(noerror),
> @@ -202,6 +204,7 @@ static struct attribute *xfs_errortag_attrs[] = {
>  	XFS_ERRORTAG_ATTR_LIST(bad_summary),
>  	XFS_ERRORTAG_ATTR_LIST(iunlink_fallback),
>  	XFS_ERRORTAG_ATTR_LIST(buf_ioerror),
> +	XFS_ERRORTAG_ATTR_LIST(reduce_max_iextents),
>  	NULL,
>  };
>  
> -- 
> 2.28.0
>