fix dblocks adjustment in growfs

fix dblocks adjustment in growfs

[Christoph Hellwig]

Hi all,

the first patch fixes a possible incorrect sb_dblocks when growfs gits
the maximum agcount or a too small AG.  The second then cleans up the
surrounding code to be better readable.

Btw, is there any reason to have this code in xfs_ag.c?  It is only used
by growfs and not at all in userspace, so having it in xfs_fsops.c would
seem more natural.

Diffstat:
 libxfs/xfs_ag.c |   44 +++++++++++++++++++++-----------------------
 libxfs/xfs_ag.h |    5 ++---
 xfs_fsops.c     |    4 +++-
 3 files changed, 26 insertions(+), 27 deletions(-)

[PATCH 1/2] xfs: pass back updated nb from xfs_growfs_compute_deltas

[Christoph Hellwig]

xfs_growfs_compute_deltas can update nb for corner cases like a number
of blocks that would create a less the minimal sized AG, or running
past the max AG limit.  Pass back the calculated value to the caller,
as it relies on that for a few things.

Fixes: a49b7ff63f98 ("xfs: Refactoring the nagcount and delta calculation")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/libxfs/xfs_ag.c | 10 +++++-----
 fs/xfs/libxfs/xfs_ag.h |  2 +-
 fs/xfs/xfs_fsops.c     |  2 +-
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index dcd2f93b6a6c..0c5f0548021f 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -866,7 +866,7 @@ xfs_ag_shrink_space(
 void
 xfs_growfs_compute_deltas(
 	struct xfs_mount	*mp,
-	xfs_rfsblock_t		nb,
+	xfs_rfsblock_t		*nb,
 	int64_t			*deltap,
 	xfs_agnumber_t		*nagcountp)
 {
@@ -874,19 +874,19 @@ xfs_growfs_compute_deltas(
 	int64_t		delta;
 	xfs_agnumber_t	nagcount;
 
-	nb_div = nb;
+	nb_div = *nb;
 	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
 	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
 		nb_div++;
 	else if (nb_mod)
-		nb = nb_div * mp->m_sb.sb_agblocks;
+		*nb = nb_div * mp->m_sb.sb_agblocks;
 
 	if (nb_div > XFS_MAX_AGNUMBER + 1) {
 		nb_div = XFS_MAX_AGNUMBER + 1;
-		nb = nb_div * mp->m_sb.sb_agblocks;
+		*nb = nb_div * mp->m_sb.sb_agblocks;
 	}
 	nagcount = nb_div;
-	delta = nb - mp->m_sb.sb_dblocks;
+	delta = *nb - mp->m_sb.sb_dblocks;
 	*deltap = delta;
 	*nagcountp = nagcount;
 }
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 16a9b43a3c27..8aa4266c5571 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -330,7 +330,7 @@ int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
 int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
 			xfs_extlen_t delta);
 void
-xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t nb,
+xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t *nb,
 			int64_t *deltap, xfs_agnumber_t *nagcountp);
 int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
 			xfs_extlen_t len);
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 8d64d904d73c..436857356a0a 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -124,7 +124,7 @@ xfs_growfs_data_private(
 			mp->m_sb.sb_rextsize);
 	if (error)
 		return error;
-	xfs_growfs_compute_deltas(mp, nb, &delta, &nagcount);
+	xfs_growfs_compute_deltas(mp, &nb, &delta, &nagcount);
 
 	/*
 	 * Reject filesystems with a single AG because they are not
-- 
2.53.0

Re: [PATCH 1/2] xfs: pass back updated nb from xfs_growfs_compute_deltas

[Darrick J. Wong]

On Mon, Jun 01, 2026 at 01:07:52PM +0200, Christoph Hellwig wrote:
> xfs_growfs_compute_deltas can update nb for corner cases like a number
> of blocks that would create a less the minimal sized AG, or running
> past the max AG limit.  Pass back the calculated value to the caller,
> as it relies on that for a few things.

A few things, like getting the fs size right after the grow?

Cc: <stable@vger.kernel.org> # v7.0

With that added,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> Fixes: a49b7ff63f98 ("xfs: Refactoring the nagcount and delta calculation")
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_ag.c | 10 +++++-----
>  fs/xfs/libxfs/xfs_ag.h |  2 +-
>  fs/xfs/xfs_fsops.c     |  2 +-
>  3 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index dcd2f93b6a6c..0c5f0548021f 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
> @@ -866,7 +866,7 @@ xfs_ag_shrink_space(
>  void
>  xfs_growfs_compute_deltas(
>  	struct xfs_mount	*mp,
> -	xfs_rfsblock_t		nb,
> +	xfs_rfsblock_t		*nb,
>  	int64_t			*deltap,
>  	xfs_agnumber_t		*nagcountp)
>  {
> @@ -874,19 +874,19 @@ xfs_growfs_compute_deltas(
>  	int64_t		delta;
>  	xfs_agnumber_t	nagcount;
>  
> -	nb_div = nb;
> +	nb_div = *nb;
>  	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
>  	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
>  		nb_div++;
>  	else if (nb_mod)
> -		nb = nb_div * mp->m_sb.sb_agblocks;
> +		*nb = nb_div * mp->m_sb.sb_agblocks;
>  
>  	if (nb_div > XFS_MAX_AGNUMBER + 1) {
>  		nb_div = XFS_MAX_AGNUMBER + 1;
> -		nb = nb_div * mp->m_sb.sb_agblocks;
> +		*nb = nb_div * mp->m_sb.sb_agblocks;
>  	}
>  	nagcount = nb_div;
> -	delta = nb - mp->m_sb.sb_dblocks;
> +	delta = *nb - mp->m_sb.sb_dblocks;
>  	*deltap = delta;
>  	*nagcountp = nagcount;
>  }
> diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> index 16a9b43a3c27..8aa4266c5571 100644
> --- a/fs/xfs/libxfs/xfs_ag.h
> +++ b/fs/xfs/libxfs/xfs_ag.h
> @@ -330,7 +330,7 @@ int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
>  int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
>  			xfs_extlen_t delta);
>  void
> -xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t nb,
> +xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t *nb,
>  			int64_t *deltap, xfs_agnumber_t *nagcountp);
>  int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
>  			xfs_extlen_t len);
> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> index 8d64d904d73c..436857356a0a 100644
> --- a/fs/xfs/xfs_fsops.c
> +++ b/fs/xfs/xfs_fsops.c
> @@ -124,7 +124,7 @@ xfs_growfs_data_private(
>  			mp->m_sb.sb_rextsize);
>  	if (error)
>  		return error;
> -	xfs_growfs_compute_deltas(mp, nb, &delta, &nagcount);
> +	xfs_growfs_compute_deltas(mp, &nb, &delta, &nagcount);
>  
>  	/*
>  	 * Reject filesystems with a single AG because they are not
> -- 
> 2.53.0
> 
> 

Re: [PATCH 1/2] xfs: pass back updated nb from xfs_growfs_compute_deltas

[Christoph Hellwig]

On Mon, Jun 01, 2026 at 09:36:40PM -0700, Darrick J. Wong wrote:
> On Mon, Jun 01, 2026 at 01:07:52PM +0200, Christoph Hellwig wrote:
> > xfs_growfs_compute_deltas can update nb for corner cases like a number
> > of blocks that would create a less the minimal sized AG, or running
> > past the max AG limit.  Pass back the calculated value to the caller,
> > as it relies on that for a few things.
> 
> A few things, like getting the fs size right after the grow?

Heh, yes.  I gues I'll have to reword this a bit to not sound silly.

[PATCH 2/2] xfs: cleanup xfs_growfs_compute_deltas

[Christoph Hellwig]

xfs_growfs_compute_deltas has an odd calling conventions, and looks
very convoluted due to the use of do_div and strangely named and typed
variables.

Rename it, make it return the agcount and let the caller calculate the
delta.  The internally use the better div_u64_rem helper and descriptive
variable names and types.  Also add a comment describing what the
function is used for.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/libxfs/xfs_ag.c | 44 ++++++++++++++++++++----------------------
 fs/xfs/libxfs/xfs_ag.h |  5 ++---
 fs/xfs/xfs_fsops.c     |  4 +++-
 3 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index 0c5f0548021f..095af128d2fb 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -863,32 +863,30 @@ xfs_ag_shrink_space(
 	return err2;
 }
 
-void
-xfs_growfs_compute_deltas(
+/*
+ * Return the agcount for the new file system size passed in *nb and adjust *nb
+ * when it has to be reduced because of maximum AG count or because it would
+ * create a below minimum size AG.
+ */
+xfs_agnumber_t
+xfs_growfs_compute_agcount(
 	struct xfs_mount	*mp,
-	xfs_rfsblock_t		*nb,
-	int64_t			*deltap,
-	xfs_agnumber_t		*nagcountp)
+	xfs_rfsblock_t		*nb)
 {
-	xfs_rfsblock_t	nb_div, nb_mod;
-	int64_t		delta;
-	xfs_agnumber_t	nagcount;
-
-	nb_div = *nb;
-	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
-	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
-		nb_div++;
-	else if (nb_mod)
-		*nb = nb_div * mp->m_sb.sb_agblocks;
-
-	if (nb_div > XFS_MAX_AGNUMBER + 1) {
-		nb_div = XFS_MAX_AGNUMBER + 1;
-		*nb = nb_div * mp->m_sb.sb_agblocks;
+	xfs_agnumber_t		agcount;
+	xfs_extlen_t		remainder;
+
+	agcount = div_u64_rem(*nb, mp->m_sb.sb_agblocks, &remainder);
+	if (agcount > XFS_MAX_AGNUMBER + 1) {
+		agcount = XFS_MAX_AGNUMBER + 1;
+		remainder = 0;
+	}
+	*nb = (xfs_rfsblock_t)agcount * mp->m_sb.sb_agblocks;
+	if (remainder >= XFS_MIN_AG_BLOCKS) {
+		*nb += remainder;
+		agcount++;
 	}
-	nagcount = nb_div;
-	delta = *nb - mp->m_sb.sb_dblocks;
-	*deltap = delta;
-	*nagcountp = nagcount;
+	return agcount;
 }
 
 /*
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 8aa4266c5571..fd22fe598931 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -329,12 +329,11 @@ struct aghdr_init_data {
 int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
 int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
 			xfs_extlen_t delta);
-void
-xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t *nb,
-			int64_t *deltap, xfs_agnumber_t *nagcountp);
 int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
 			xfs_extlen_t len);
 int xfs_ag_get_geometry(struct xfs_perag *pag, struct xfs_ag_geometry *ageo);
+xfs_agnumber_t xfs_growfs_compute_agcount(struct xfs_mount *mp,
+		xfs_rfsblock_t *nb);
 
 static inline xfs_fsblock_t
 xfs_agbno_to_fsb(
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 436857356a0a..67624a804a7f 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -124,7 +124,9 @@ xfs_growfs_data_private(
 			mp->m_sb.sb_rextsize);
 	if (error)
 		return error;
-	xfs_growfs_compute_deltas(mp, &nb, &delta, &nagcount);
+
+	nagcount = xfs_growfs_compute_agcount(mp, &nb);
+	delta = nb - mp->m_sb.sb_dblocks;
 
 	/*
 	 * Reject filesystems with a single AG because they are not
-- 
2.53.0

Re: [PATCH 2/2] xfs: cleanup xfs_growfs_compute_deltas

[Darrick J. Wong]

On Mon, Jun 01, 2026 at 01:07:53PM +0200, Christoph Hellwig wrote:
> xfs_growfs_compute_deltas has an odd calling conventions, and looks
> very convoluted due to the use of do_div and strangely named and typed
> variables.
> 
> Rename it, make it return the agcount and let the caller calculate the
> delta.  The internally use the better div_u64_rem helper and descriptive
> variable names and types.  Also add a comment describing what the
> function is used for.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

AFAICT the logic is the same before and after, so
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

Though I half wonder if that XFS_MAX_AGNUMBER+1 comparison is really
correct.  MAX_AGNUMBER is defined to be ((xfs_agnumber_t)-2) so we're
checking if an unsigned 32-bit number is greater than 0xFFFFFFFF?
Which is also NULLAGNUMBER?

--D

> ---
>  fs/xfs/libxfs/xfs_ag.c | 44 ++++++++++++++++++++----------------------
>  fs/xfs/libxfs/xfs_ag.h |  5 ++---
>  fs/xfs/xfs_fsops.c     |  4 +++-
>  3 files changed, 26 insertions(+), 27 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index 0c5f0548021f..095af128d2fb 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
> @@ -863,32 +863,30 @@ xfs_ag_shrink_space(
>  	return err2;
>  }
>  
> -void
> -xfs_growfs_compute_deltas(
> +/*
> + * Return the agcount for the new file system size passed in *nb and adjust *nb
> + * when it has to be reduced because of maximum AG count or because it would
> + * create a below minimum size AG.
> + */
> +xfs_agnumber_t
> +xfs_growfs_compute_agcount(
>  	struct xfs_mount	*mp,
> -	xfs_rfsblock_t		*nb,
> -	int64_t			*deltap,
> -	xfs_agnumber_t		*nagcountp)
> +	xfs_rfsblock_t		*nb)
>  {
> -	xfs_rfsblock_t	nb_div, nb_mod;
> -	int64_t		delta;
> -	xfs_agnumber_t	nagcount;
> -
> -	nb_div = *nb;
> -	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
> -	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
> -		nb_div++;
> -	else if (nb_mod)
> -		*nb = nb_div * mp->m_sb.sb_agblocks;
> -
> -	if (nb_div > XFS_MAX_AGNUMBER + 1) {
> -		nb_div = XFS_MAX_AGNUMBER + 1;
> -		*nb = nb_div * mp->m_sb.sb_agblocks;
> +	xfs_agnumber_t		agcount;
> +	xfs_extlen_t		remainder;
> +
> +	agcount = div_u64_rem(*nb, mp->m_sb.sb_agblocks, &remainder);
> +	if (agcount > XFS_MAX_AGNUMBER + 1) {
> +		agcount = XFS_MAX_AGNUMBER + 1;
> +		remainder = 0;
> +	}
> +	*nb = (xfs_rfsblock_t)agcount * mp->m_sb.sb_agblocks;
> +	if (remainder >= XFS_MIN_AG_BLOCKS) {
> +		*nb += remainder;
> +		agcount++;
>  	}
> -	nagcount = nb_div;
> -	delta = *nb - mp->m_sb.sb_dblocks;
> -	*deltap = delta;
> -	*nagcountp = nagcount;
> +	return agcount;
>  }
>  
>  /*
> diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> index 8aa4266c5571..fd22fe598931 100644
> --- a/fs/xfs/libxfs/xfs_ag.h
> +++ b/fs/xfs/libxfs/xfs_ag.h
> @@ -329,12 +329,11 @@ struct aghdr_init_data {
>  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
>  int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
>  			xfs_extlen_t delta);
> -void
> -xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t *nb,
> -			int64_t *deltap, xfs_agnumber_t *nagcountp);
>  int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
>  			xfs_extlen_t len);
>  int xfs_ag_get_geometry(struct xfs_perag *pag, struct xfs_ag_geometry *ageo);
> +xfs_agnumber_t xfs_growfs_compute_agcount(struct xfs_mount *mp,
> +		xfs_rfsblock_t *nb);
>  
>  static inline xfs_fsblock_t
>  xfs_agbno_to_fsb(
> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> index 436857356a0a..67624a804a7f 100644
> --- a/fs/xfs/xfs_fsops.c
> +++ b/fs/xfs/xfs_fsops.c
> @@ -124,7 +124,9 @@ xfs_growfs_data_private(
>  			mp->m_sb.sb_rextsize);
>  	if (error)
>  		return error;
> -	xfs_growfs_compute_deltas(mp, &nb, &delta, &nagcount);
> +
> +	nagcount = xfs_growfs_compute_agcount(mp, &nb);
> +	delta = nb - mp->m_sb.sb_dblocks;
>  
>  	/*
>  	 * Reject filesystems with a single AG because they are not
> -- 
> 2.53.0
> 
> 

Re: [PATCH 2/2] xfs: cleanup xfs_growfs_compute_deltas

[Christoph Hellwig]

On Mon, Jun 01, 2026 at 09:42:03PM -0700, Darrick J. Wong wrote:
> AFAICT the logic is the same before and after, so
> Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
> 
> Though I half wonder if that XFS_MAX_AGNUMBER+1 comparison is really
> correct.  MAX_AGNUMBER is defined to be ((xfs_agnumber_t)-2) so we're
> checking if an unsigned 32-bit number is greater than 0xFFFFFFFF?
> Which is also NULLAGNUMBER?

Not this this is the count and the number.  This also is the only
use of MAX_AGNUMBER in the kernel and xfsprogs has a copy of it
defined in XFS_MAX_AGNUMBER.  I'll see if there is a cleaner way
to express this, and the fact that agnumber is now a 32-bit value
might also mess things up a bit.

fix dblocks adjustment in growfs v2

[Christoph Hellwig]

Hi all,

the first patch fixes a possible incorrect sb_dblocks when growfs gits
the maximum agcount or a too small AG.  The second then cleans up the
surrounding code to be better readable.

Btw, is there any reason to have this code in xfs_ag.c?  It is only used
by growfs and not at all in userspace, so having it in xfs_fsops.c would
seem more natural.

Changes since v1:
 - clarify what we wrong in the commit log for patch 1
 - use a 64-bit agno variable in patch 2 to deal with 32-bit overflows

Diffstat:
 libxfs/xfs_ag.c |   44 +++++++++++++++++++++-----------------------
 libxfs/xfs_ag.h |    5 ++---
 xfs_fsops.c     |    4 +++-
 3 files changed, 26 insertions(+), 27 deletions(-)

[PATCH 1/2] xfs: pass back updated nb from xfs_growfs_compute_deltas

[Christoph Hellwig]

xfs_growfs_compute_deltas can update nb for corner cases like a number
of blocks that would create a less the minimal sized AG, or running
past the max AG limit.  Pass back the calculated value to the caller,
as it relies on to calculate the new numeber of perag structures.

Note that the grown file system size is not affected by this
miscaculation as it uses the passed back delta value.

Fixes: a49b7ff63f98 ("xfs: Refactoring the nagcount and delta calculation")
Cc: <stable@vger.kernel.org> # v7.0
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
---
 fs/xfs/libxfs/xfs_ag.c | 10 +++++-----
 fs/xfs/libxfs/xfs_ag.h |  2 +-
 fs/xfs/xfs_fsops.c     |  2 +-
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index dcd2f93b6a6c..0c5f0548021f 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -866,7 +866,7 @@ xfs_ag_shrink_space(
 void
 xfs_growfs_compute_deltas(
 	struct xfs_mount	*mp,
-	xfs_rfsblock_t		nb,
+	xfs_rfsblock_t		*nb,
 	int64_t			*deltap,
 	xfs_agnumber_t		*nagcountp)
 {
@@ -874,19 +874,19 @@ xfs_growfs_compute_deltas(
 	int64_t		delta;
 	xfs_agnumber_t	nagcount;
 
-	nb_div = nb;
+	nb_div = *nb;
 	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
 	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
 		nb_div++;
 	else if (nb_mod)
-		nb = nb_div * mp->m_sb.sb_agblocks;
+		*nb = nb_div * mp->m_sb.sb_agblocks;
 
 	if (nb_div > XFS_MAX_AGNUMBER + 1) {
 		nb_div = XFS_MAX_AGNUMBER + 1;
-		nb = nb_div * mp->m_sb.sb_agblocks;
+		*nb = nb_div * mp->m_sb.sb_agblocks;
 	}
 	nagcount = nb_div;
-	delta = nb - mp->m_sb.sb_dblocks;
+	delta = *nb - mp->m_sb.sb_dblocks;
 	*deltap = delta;
 	*nagcountp = nagcount;
 }
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 16a9b43a3c27..8aa4266c5571 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -330,7 +330,7 @@ int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
 int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
 			xfs_extlen_t delta);
 void
-xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t nb,
+xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t *nb,
 			int64_t *deltap, xfs_agnumber_t *nagcountp);
 int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
 			xfs_extlen_t len);
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 8d64d904d73c..436857356a0a 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -124,7 +124,7 @@ xfs_growfs_data_private(
 			mp->m_sb.sb_rextsize);
 	if (error)
 		return error;
-	xfs_growfs_compute_deltas(mp, nb, &delta, &nagcount);
+	xfs_growfs_compute_deltas(mp, &nb, &delta, &nagcount);
 
 	/*
 	 * Reject filesystems with a single AG because they are not
-- 
2.53.0

fix dblocks adjustment in growfs v3

[Christoph Hellwig]

Hi all,

the first patch fixes a possible incorrect sb_dblocks when growfs gits
the maximum agcount or a too small AG.  The second then cleans up the
surrounding code to be better readable.

Btw, is there any reason to have this code in xfs_ag.c?  It is only used
by growfs and not at all in userspace, so having it in xfs_fsops.c would
seem more natural.

Changes since v2:
 - another too large overflow fix
 - spelling fixes

Changes since v1:
 - clarify what we wrong in the commit log for patch 1
 - use a 64-bit agno variable in patch 2 to deal with 32-bit overflows

Diffstat:
 libxfs/xfs_ag.c |   44 +++++++++++++++++++++-----------------------
 libxfs/xfs_ag.h |    5 ++---
 xfs_fsops.c     |    4 +++-
 3 files changed, 26 insertions(+), 27 deletions(-)

[PATCH 1/2] xfs: pass back updated nb from xfs_growfs_compute_deltas

[Christoph Hellwig]

xfs_growfs_compute_deltas can update nb for corner cases like a number
of blocks that would create a less the minimal sized AG, or running
past the max AG limit.  Pass back the calculated value to the caller,
as it relies on to calculate the new number of perag structures.

Note that the grown file system size is not affected by this
miscalculation as it uses the passed back delta value.

Fixes: a49b7ff63f98 ("xfs: Refactoring the nagcount and delta calculation")
Cc: <stable@vger.kernel.org> # v7.0
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
---
 fs/xfs/libxfs/xfs_ag.c | 10 +++++-----
 fs/xfs/libxfs/xfs_ag.h |  2 +-
 fs/xfs/xfs_fsops.c     |  2 +-
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index dcd2f93b6a6c..0c5f0548021f 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -866,7 +866,7 @@ xfs_ag_shrink_space(
 void
 xfs_growfs_compute_deltas(
 	struct xfs_mount	*mp,
-	xfs_rfsblock_t		nb,
+	xfs_rfsblock_t		*nb,
 	int64_t			*deltap,
 	xfs_agnumber_t		*nagcountp)
 {
@@ -874,19 +874,19 @@ xfs_growfs_compute_deltas(
 	int64_t		delta;
 	xfs_agnumber_t	nagcount;
 
-	nb_div = nb;
+	nb_div = *nb;
 	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
 	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
 		nb_div++;
 	else if (nb_mod)
-		nb = nb_div * mp->m_sb.sb_agblocks;
+		*nb = nb_div * mp->m_sb.sb_agblocks;
 
 	if (nb_div > XFS_MAX_AGNUMBER + 1) {
 		nb_div = XFS_MAX_AGNUMBER + 1;
-		nb = nb_div * mp->m_sb.sb_agblocks;
+		*nb = nb_div * mp->m_sb.sb_agblocks;
 	}
 	nagcount = nb_div;
-	delta = nb - mp->m_sb.sb_dblocks;
+	delta = *nb - mp->m_sb.sb_dblocks;
 	*deltap = delta;
 	*nagcountp = nagcount;
 }
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 16a9b43a3c27..8aa4266c5571 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -330,7 +330,7 @@ int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
 int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
 			xfs_extlen_t delta);
 void
-xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t nb,
+xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t *nb,
 			int64_t *deltap, xfs_agnumber_t *nagcountp);
 int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
 			xfs_extlen_t len);
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 8d64d904d73c..436857356a0a 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -124,7 +124,7 @@ xfs_growfs_data_private(
 			mp->m_sb.sb_rextsize);
 	if (error)
 		return error;
-	xfs_growfs_compute_deltas(mp, nb, &delta, &nagcount);
+	xfs_growfs_compute_deltas(mp, &nb, &delta, &nagcount);
 
 	/*
 	 * Reject filesystems with a single AG because they are not
-- 
2.53.0