diff mbox series

[rdma-next,v3,2/3] lib/scatterlist: Fix wrong update of orig_nents

Message ID 460ae18dd1bbd6c1175e75f5d4e51ddb449acf8d.1627551226.git.leonro@nvidia.com (mailing list archive)
State New, archived
Headers show
Series SG fix together with update to RDMA umem | expand

Commit Message

Leon Romanovsky July 29, 2021, 9:39 a.m. UTC
From: Maor Gottlieb <maorg@nvidia.com>

orig_nents should represent the number of entries with pages,
but __sg_alloc_table_from_pages sets orig_nents as the number of
total entries in the table. This is wrong when the API is used for
dynamic allocation where not all the table entries are mapped with
pages. It wasn't observed until now, since RDMA umem who uses this
API in the dynamic form doesn't use orig_nents implicit or explicit
by the scatterlist APIs.

Fix it by changing the append API to track the SG append table
state and have an API to free the append table according to the
total number of entries in the table.
Now all APIs set orig_nents as number of enries with pages.

Fixes: 07da1223ec93 ("lib/scatterlist: Add support in dynamic allocation of SG table from pages")
Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 drivers/infiniband/core/umem.c   |  34 ++++---
 include/linux/scatterlist.h      |  17 +++-
 include/rdma/ib_umem.h           |   1 +
 lib/scatterlist.c                | 161 +++++++++++++++++++------------
 tools/testing/scatterlist/main.c |  45 +++++----
 5 files changed, 154 insertions(+), 104 deletions(-)

Comments

Jason Gunthorpe Aug. 20, 2021, 3:54 p.m. UTC | #1
On Thu, Jul 29, 2021 at 12:39:12PM +0300, Leon Romanovsky wrote:

> +/**
> + * __sg_free_table - Free a previously mapped sg table
> + * @table:	The sg table header to use
> + * @max_ents:	The maximum number of entries per single scatterlist
> + * @total_ents:	The total number of entries in the table
> + * @nents_first_chunk: Number of entries int the (preallocated) first
> + *                     scatterlist chunk, 0 means no such preallocated
> + *                     first chunk
> + * @free_fn:	Free function
> + *
> + *  Description:
> + *    Free an sg table previously allocated and setup with
> + *    __sg_alloc_table().  The @max_ents value must be identical to
> + *    that previously used with __sg_alloc_table().
> + *
> + **/
> +void __sg_free_table(struct sg_table *table, unsigned int max_ents,
> +		     unsigned int nents_first_chunk, sg_free_fn *free_fn)
> +{
> +	sg_free_table_entries(table, max_ents, nents_first_chunk, free_fn,
> +			      table->orig_nents);
> +}
>  EXPORT_SYMBOL(__sg_free_table);

This is getting a bit indirect, there is only one caller of
__sg_free_table() in sg_pool.c, so may as well just export
sg_free_table_entries have have it use that directly.

Jason
Jason Gunthorpe Aug. 20, 2021, 3:57 p.m. UTC | #2
On Fri, Aug 20, 2021 at 12:54:25PM -0300, Jason Gunthorpe wrote:
> On Thu, Jul 29, 2021 at 12:39:12PM +0300, Leon Romanovsky wrote:
> 
> > +/**
> > + * __sg_free_table - Free a previously mapped sg table
> > + * @table:	The sg table header to use
> > + * @max_ents:	The maximum number of entries per single scatterlist
> > + * @total_ents:	The total number of entries in the table
> > + * @nents_first_chunk: Number of entries int the (preallocated) first
> > + *                     scatterlist chunk, 0 means no such preallocated
> > + *                     first chunk
> > + * @free_fn:	Free function
> > + *
> > + *  Description:
> > + *    Free an sg table previously allocated and setup with
> > + *    __sg_alloc_table().  The @max_ents value must be identical to
> > + *    that previously used with __sg_alloc_table().
> > + *
> > + **/
> > +void __sg_free_table(struct sg_table *table, unsigned int max_ents,
> > +		     unsigned int nents_first_chunk, sg_free_fn *free_fn)
> > +{
> > +	sg_free_table_entries(table, max_ents, nents_first_chunk, free_fn,
> > +			      table->orig_nents);
> > +}
> >  EXPORT_SYMBOL(__sg_free_table);
> 
> This is getting a bit indirect, there is only one caller of
> __sg_free_table() in sg_pool.c, so may as well just export
> sg_free_table_entries have have it use that directly.

And further since sg_free_table_entries() doesn't actually use table->
except for the SGL it should probably be called sg_free_table_sgl()

Jason
Maor Gottlieb Aug. 23, 2021, 11:09 a.m. UTC | #3
On 8/20/2021 6:54 PM, Jason Gunthorpe wrote:
> On Thu, Jul 29, 2021 at 12:39:12PM +0300, Leon Romanovsky wrote:
>
>> +/**
>> + * __sg_free_table - Free a previously mapped sg table
>> + * @table:	The sg table header to use
>> + * @max_ents:	The maximum number of entries per single scatterlist
>> + * @total_ents:	The total number of entries in the table
>> + * @nents_first_chunk: Number of entries int the (preallocated) first
>> + *                     scatterlist chunk, 0 means no such preallocated
>> + *                     first chunk
>> + * @free_fn:	Free function
>> + *
>> + *  Description:
>> + *    Free an sg table previously allocated and setup with
>> + *    __sg_alloc_table().  The @max_ents value must be identical to
>> + *    that previously used with __sg_alloc_table().
>> + *
>> + **/
>> +void __sg_free_table(struct sg_table *table, unsigned int max_ents,
>> +		     unsigned int nents_first_chunk, sg_free_fn *free_fn)
>> +{
>> +	sg_free_table_entries(table, max_ents, nents_first_chunk, free_fn,
>> +			      table->orig_nents);
>> +}
>>   EXPORT_SYMBOL(__sg_free_table);
> This is getting a bit indirect, there is only one caller of
> __sg_free_table() in sg_pool.c, so may as well just export
> sg_free_table_entries have have it use that directly.
>
> Jason

So I can just extend __sg_free_table to get number of entries. What do 
you think?
Jason Gunthorpe Aug. 23, 2021, 12:45 p.m. UTC | #4
On Mon, Aug 23, 2021 at 02:09:37PM +0300, Maor Gottlieb wrote:
> 
> On 8/20/2021 6:54 PM, Jason Gunthorpe wrote:
> > On Thu, Jul 29, 2021 at 12:39:12PM +0300, Leon Romanovsky wrote:
> > 
> > > +/**
> > > + * __sg_free_table - Free a previously mapped sg table
> > > + * @table:	The sg table header to use
> > > + * @max_ents:	The maximum number of entries per single scatterlist
> > > + * @total_ents:	The total number of entries in the table
> > > + * @nents_first_chunk: Number of entries int the (preallocated) first
> > > + *                     scatterlist chunk, 0 means no such preallocated
> > > + *                     first chunk
> > > + * @free_fn:	Free function
> > > + *
> > > + *  Description:
> > > + *    Free an sg table previously allocated and setup with
> > > + *    __sg_alloc_table().  The @max_ents value must be identical to
> > > + *    that previously used with __sg_alloc_table().
> > > + *
> > > + **/
> > > +void __sg_free_table(struct sg_table *table, unsigned int max_ents,
> > > +		     unsigned int nents_first_chunk, sg_free_fn *free_fn)
> > > +{
> > > +	sg_free_table_entries(table, max_ents, nents_first_chunk, free_fn,
> > > +			      table->orig_nents);
> > > +}
> > >   EXPORT_SYMBOL(__sg_free_table);
> > This is getting a bit indirect, there is only one caller of
> > __sg_free_table() in sg_pool.c, so may as well just export
> > sg_free_table_entries have have it use that directly.
> 
> So I can just extend __sg_free_table to get number of entries. What do you
> think?

Isn't the point here that different paths to __sg_free_table require
different entries? What do you mean?

Jason
Jason Gunthorpe Aug. 23, 2021, 1:54 p.m. UTC | #5
On Mon, Aug 23, 2021 at 04:45:45PM +0300, Maor Gottlieb wrote:
> 
> On 8/23/2021 3:45 PM, Jason Gunthorpe wrote:
> > On Mon, Aug 23, 2021 at 02:09:37PM +0300, Maor Gottlieb wrote:
> > > On 8/20/2021 6:54 PM, Jason Gunthorpe wrote:
> > > > On Thu, Jul 29, 2021 at 12:39:12PM +0300, Leon Romanovsky wrote:
> > > > 
> > > > > +/**
> > > > > + * __sg_free_table - Free a previously mapped sg table
> > > > > + * @table:	The sg table header to use
> > > > > + * @max_ents:	The maximum number of entries per single scatterlist
> > > > > + * @total_ents:	The total number of entries in the table
> > > > > + * @nents_first_chunk: Number of entries int the (preallocated) first
> > > > > + *                     scatterlist chunk, 0 means no such preallocated
> > > > > + *                     first chunk
> > > > > + * @free_fn:	Free function
> > > > > + *
> > > > > + *  Description:
> > > > > + *    Free an sg table previously allocated and setup with
> > > > > + *    __sg_alloc_table().  The @max_ents value must be identical to
> > > > > + *    that previously used with __sg_alloc_table().
> > > > > + *
> > > > > + **/
> > > > > +void __sg_free_table(struct sg_table *table, unsigned int max_ents,
> > > > > +		     unsigned int nents_first_chunk, sg_free_fn *free_fn)
> > > > > +{
> > > > > +	sg_free_table_entries(table, max_ents, nents_first_chunk, free_fn,
> > > > > +			      table->orig_nents);
> > > > > +}
> > > > >    EXPORT_SYMBOL(__sg_free_table);
> > > > This is getting a bit indirect, there is only one caller of
> > > > __sg_free_table() in sg_pool.c, so may as well just export
> > > > sg_free_table_entries have have it use that directly.
> > > So I can just extend __sg_free_table to get number of entries. What do you
> > > think?
> > Isn't the point here that different paths to __sg_free_table require
> > different entries? What do you mean?
> 
> I mean that  __sg_free_table will get the number of entries. sg_pool will
> call it with table->orig_nents and sg_free_append_table will call it with
> with total_nents.

That is sort of what you've done, just renamed __sg_free_table to
sg_free_table_entries in the process, which seem fine enough

Jason
diff mbox series

Patch

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index b741758e528f..42481e7a72e8 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -59,7 +59,7 @@  static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
 		unpin_user_page_range_dirty_lock(sg_page(sg),
 			DIV_ROUND_UP(sg->length, PAGE_SIZE), make_dirty);
 
-	sg_free_table(&umem->sg_head);
+	sg_free_append_table(&umem->sgt_append);
 }
 
 /**
@@ -155,8 +155,7 @@  struct ib_umem *ib_umem_get(struct ib_device *device, unsigned long addr,
 	unsigned long dma_attr = 0;
 	struct mm_struct *mm;
 	unsigned long npages;
-	int ret;
-	struct scatterlist *sg = NULL;
+	int pinned, ret;
 	unsigned int gup_flags = FOLL_WRITE;
 
 	/*
@@ -216,28 +215,33 @@  struct ib_umem *ib_umem_get(struct ib_device *device, unsigned long addr,
 
 	while (npages) {
 		cond_resched();
-		ret = pin_user_pages_fast(cur_base,
+		pinned = pin_user_pages_fast(cur_base,
 					  min_t(unsigned long, npages,
 						PAGE_SIZE /
 						sizeof(struct page *)),
 					  gup_flags | FOLL_LONGTERM, page_list);
-		if (ret < 0)
+		if (pinned < 0) {
+			ret = pinned;
 			goto umem_release;
+		}
 
-		cur_base += ret * PAGE_SIZE;
-		npages -= ret;
-		sg = sg_alloc_append_table_from_pages(&umem->sg_head, page_list,
-				ret, 0, ret << PAGE_SHIFT,
-				ib_dma_max_seg_size(device), sg, npages,
-				GFP_KERNEL);
-		umem->sg_nents = umem->sg_head.nents;
-		if (IS_ERR(sg)) {
-			unpin_user_pages_dirty_lock(page_list, ret, 0);
-			ret = PTR_ERR(sg);
+		cur_base += pinned * PAGE_SIZE;
+		npages -= pinned;
+		ret = sg_alloc_append_table_from_pages(
+			&umem->sgt_append, page_list, pinned, 0,
+			pinned << PAGE_SHIFT, ib_dma_max_seg_size(device),
+			npages, GFP_KERNEL);
+		umem->sg_nents = umem->sgt_append.sgt.nents;
+		if (ret) {
+			memcpy(&umem->sg_head.sgl, &umem->sgt_append.sgt,
+			       sizeof(umem->sgt_append.sgt));
+			unpin_user_pages_dirty_lock(page_list, pinned, 0);
 			goto umem_release;
 		}
 	}
 
+	memcpy(&umem->sg_head.sgl, &umem->sgt_append.sgt,
+	       sizeof(umem->sgt_append.sgt));
 	if (access & IB_ACCESS_RELAXED_ORDERING)
 		dma_attr |= DMA_ATTR_WEAK_ORDERING;
 
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 5c700f2a0d18..0c7aa5ccebfc 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -39,6 +39,12 @@  struct sg_table {
 	unsigned int orig_nents;	/* original size of list */
 };
 
+struct sg_append_table {
+	struct sg_table sgt;		/* The scatter list table */
+	struct scatterlist *prv;	/* last populated sge in the table */
+	unsigned int total_nents;	/* Total entries in the table */
+};
+
 /*
  * Notes on SG table design.
  *
@@ -282,14 +288,15 @@  typedef void (sg_free_fn)(struct scatterlist *, unsigned int);
 void __sg_free_table(struct sg_table *, unsigned int, unsigned int,
 		     sg_free_fn *);
 void sg_free_table(struct sg_table *);
+void sg_free_append_table(struct sg_append_table *sgt);
 int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int,
 		     struct scatterlist *, unsigned int, gfp_t, sg_alloc_fn *);
 int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
-struct scatterlist *sg_alloc_append_table_from_pages(struct sg_table *sgt,
-		struct page **pages, unsigned int n_pages, unsigned int offset,
-		unsigned long size, unsigned int max_segment,
-		struct scatterlist *prv, unsigned int left_pages,
-		gfp_t gfp_mask);
+int sg_alloc_append_table_from_pages(struct sg_append_table *sgt,
+				     struct page **pages, unsigned int n_pages,
+				     unsigned int offset, unsigned long size,
+				     unsigned int max_segment,
+				     unsigned int left_pages, gfp_t gfp_mask);
 int sg_alloc_table_from_pages_segment(struct sg_table *sgt, struct page **pages,
 				      unsigned int n_pages, unsigned int offset,
 				      unsigned long size,
diff --git a/include/rdma/ib_umem.h b/include/rdma/ib_umem.h
index 676c57f5ca80..33cb23b2ee3c 100644
--- a/include/rdma/ib_umem.h
+++ b/include/rdma/ib_umem.h
@@ -26,6 +26,7 @@  struct ib_umem {
 	u32 is_odp : 1;
 	u32 is_dmabuf : 1;
 	struct work_struct	work;
+	struct sg_append_table  sgt_append;
 	struct sg_table sg_head;
 	int             nmap;
 	unsigned int    sg_nents;
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 611c63d4a958..b96b71c762b6 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -175,22 +175,9 @@  static void sg_kfree(struct scatterlist *sg, unsigned int nents)
 		kfree(sg);
 }
 
-/**
- * __sg_free_table - Free a previously mapped sg table
- * @table:	The sg table header to use
- * @max_ents:	The maximum number of entries per single scatterlist
- * @nents_first_chunk: Number of entries int the (preallocated) first
- * 	scatterlist chunk, 0 means no such preallocated first chunk
- * @free_fn:	Free function
- *
- *  Description:
- *    Free an sg table previously allocated and setup with
- *    __sg_alloc_table().  The @max_ents value must be identical to
- *    that previously used with __sg_alloc_table().
- *
- **/
-void __sg_free_table(struct sg_table *table, unsigned int max_ents,
-		     unsigned int nents_first_chunk, sg_free_fn *free_fn)
+static void sg_free_table_entries(struct sg_table *table, unsigned int max_ents,
+				  unsigned int nents_first_chunk,
+				  sg_free_fn *free_fn, unsigned int num_entries)
 {
 	struct scatterlist *sgl, *next;
 	unsigned curr_max_ents = nents_first_chunk ?: max_ents;
@@ -199,8 +186,8 @@  void __sg_free_table(struct sg_table *table, unsigned int max_ents,
 		return;
 
 	sgl = table->sgl;
-	while (table->orig_nents) {
-		unsigned int alloc_size = table->orig_nents;
+	while (num_entries) {
+		unsigned int alloc_size = num_entries;
 		unsigned int sg_size;
 
 		/*
@@ -218,7 +205,7 @@  void __sg_free_table(struct sg_table *table, unsigned int max_ents,
 			next = NULL;
 		}
 
-		table->orig_nents -= sg_size;
+		num_entries -= sg_size;
 		if (nents_first_chunk)
 			nents_first_chunk = 0;
 		else
@@ -229,6 +216,41 @@  void __sg_free_table(struct sg_table *table, unsigned int max_ents,
 
 	table->sgl = NULL;
 }
+
+/**
+ * sg_free_append_table - Free a previously allocated append sg table.
+ * @table:	 The mapped sg append table header
+ *
+ **/
+void sg_free_append_table(struct sg_append_table *table)
+{
+	sg_free_table_entries(&table->sgt, SG_MAX_SINGLE_ALLOC, false, sg_kfree,
+			      table->total_nents);
+}
+EXPORT_SYMBOL(sg_free_append_table);
+
+/**
+ * __sg_free_table - Free a previously mapped sg table
+ * @table:	The sg table header to use
+ * @max_ents:	The maximum number of entries per single scatterlist
+ * @total_ents:	The total number of entries in the table
+ * @nents_first_chunk: Number of entries int the (preallocated) first
+ *                     scatterlist chunk, 0 means no such preallocated
+ *                     first chunk
+ * @free_fn:	Free function
+ *
+ *  Description:
+ *    Free an sg table previously allocated and setup with
+ *    __sg_alloc_table().  The @max_ents value must be identical to
+ *    that previously used with __sg_alloc_table().
+ *
+ **/
+void __sg_free_table(struct sg_table *table, unsigned int max_ents,
+		     unsigned int nents_first_chunk, sg_free_fn *free_fn)
+{
+	sg_free_table_entries(table, max_ents, nents_first_chunk, free_fn,
+			      table->orig_nents);
+}
 EXPORT_SYMBOL(__sg_free_table);
 
 /**
@@ -238,7 +260,8 @@  EXPORT_SYMBOL(__sg_free_table);
  **/
 void sg_free_table(struct sg_table *table)
 {
-	__sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
+	sg_free_table_entries(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree,
+			      table->orig_nents);
 }
 EXPORT_SYMBOL(sg_free_table);
 
@@ -365,7 +388,7 @@  int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
 }
 EXPORT_SYMBOL(sg_alloc_table);
 
-static struct scatterlist *get_next_sg(struct sg_table *table,
+static struct scatterlist *get_next_sg(struct sg_append_table *table,
 				       struct scatterlist *cur,
 				       unsigned long needed_sges,
 				       gfp_t gfp_mask)
@@ -386,54 +409,52 @@  static struct scatterlist *get_next_sg(struct sg_table *table,
 		return ERR_PTR(-ENOMEM);
 	sg_init_table(new_sg, alloc_size);
 	if (cur) {
+		table->total_nents += alloc_size - 1;
 		__sg_chain(next_sg, new_sg);
-		table->orig_nents += alloc_size - 1;
 	} else {
-		table->sgl = new_sg;
-		table->orig_nents = alloc_size;
-		table->nents = 0;
+		table->sgt.sgl = new_sg;
+		table->total_nents = alloc_size;
 	}
 	return new_sg;
 }
 
 /**
- * sg_alloc_append_table_from_pages - Allocate and initialize an sg table from
- *			         an array of pages
- * @sgt:	 The sg table header to use
- * @pages:	 Pointer to an array of page pointers
- * @n_pages:	 Number of pages in the pages array
+ * sg_alloc_append_table_from_pages - Allocate and initialize an append sg
+ *                                    table from an array of pages
+ * @sgt_append:  The sg append table to use
+ * @pages:       Pointer to an array of page pointers
+ * @n_pages:     Number of pages in the pages array
  * @offset:      Offset from start of the first page to the start of a buffer
  * @size:        Number of valid bytes in the buffer (after offset)
  * @max_segment: Maximum size of a scatterlist element in bytes
- * @prv:	 Last populated sge in sgt
  * @left_pages:  Left pages caller have to set after this call
  * @gfp_mask:	 GFP allocation mask
  *
  * Description:
- *    If @prv is NULL, allocate and initialize an sg table from a list of pages,
- *    else reuse the scatterlist passed in at @prv.
- *    Contiguous ranges of the pages are squashed into a single scatterlist
- *    entry up to the maximum size specified in @max_segment.  A user may
- *    provide an offset at a start and a size of valid data in a buffer
- *    specified by the page array.
+ *    In the first call it allocate and initialize an sg table from a list of
+ *    pages, else reuse the scatterlist from sgt_append. Contiguous ranges of
+ *    the pages are squashed into a single scatterlist entry up to the maximum
+ *    size specified in @max_segment.  A user may provide an offset at a start
+ *    and a size of valid data in a buffer specified by the page array. The
+ *    returned sg table is released by sg_free_append_table
  *
  * Returns:
- *   Last SGE in sgt on success, PTR_ERR on otherwise.
- *   The allocation in @sgt must be released by sg_free_table.
+ *   0 on success, negative error on failure
  *
  * Notes:
  *   If this function returns non-0 (eg failure), the caller must call
- *   sg_free_table() to cleanup any leftover allocations.
+ *   sg_free_append_table() to cleanup any leftover allocations.
+ *
+ *   In the fist call, sgt_append must by initialized.
  */
-struct scatterlist *sg_alloc_append_table_from_pages(struct sg_table *sgt,
+int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
 		struct page **pages, unsigned int n_pages, unsigned int offset,
 		unsigned long size, unsigned int max_segment,
-		struct scatterlist *prv, unsigned int left_pages,
-		gfp_t gfp_mask)
+		unsigned int left_pages, gfp_t gfp_mask)
 {
 	unsigned int chunks, cur_page, seg_len, i, prv_len = 0;
 	unsigned int added_nents = 0;
-	struct scatterlist *s = prv;
+	struct scatterlist *s = sgt_append->prv;
 
 	/*
 	 * The algorithm below requires max_segment to be aligned to PAGE_SIZE
@@ -441,25 +462,26 @@  struct scatterlist *sg_alloc_append_table_from_pages(struct sg_table *sgt,
 	 */
 	max_segment = ALIGN_DOWN(max_segment, PAGE_SIZE);
 	if (WARN_ON(max_segment < PAGE_SIZE))
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 
-	if (IS_ENABLED(CONFIG_ARCH_NO_SG_CHAIN) && prv)
-		return ERR_PTR(-EOPNOTSUPP);
+	if (IS_ENABLED(CONFIG_ARCH_NO_SG_CHAIN) && sgt_append->prv)
+		return -EOPNOTSUPP;
 
-	if (prv) {
-		unsigned long paddr = (page_to_pfn(sg_page(prv)) * PAGE_SIZE +
-				       prv->offset + prv->length) /
-				      PAGE_SIZE;
+	if (sgt_append->prv) {
+		unsigned long paddr =
+			(page_to_pfn(sg_page(sgt_append->prv)) * PAGE_SIZE +
+			 sgt_append->prv->offset + sgt_append->prv->length) /
+			PAGE_SIZE;
 
 		if (WARN_ON(offset))
-			return ERR_PTR(-EINVAL);
+			return -EINVAL;
 
 		/* Merge contiguous pages into the last SG */
-		prv_len = prv->length;
+		prv_len = sgt_append->prv->length;
 		while (n_pages && page_to_pfn(pages[0]) == paddr) {
-			if (prv->length + PAGE_SIZE > max_segment)
+			if (sgt_append->prv->length + PAGE_SIZE > max_segment)
 				break;
-			prv->length += PAGE_SIZE;
+			sgt_append->prv->length += PAGE_SIZE;
 			paddr++;
 			pages++;
 			n_pages--;
@@ -496,15 +518,16 @@  struct scatterlist *sg_alloc_append_table_from_pages(struct sg_table *sgt,
 		}
 
 		/* Pass how many chunks might be left */
-		s = get_next_sg(sgt, s, chunks - i + left_pages, gfp_mask);
+		s = get_next_sg(sgt_append, s, chunks - i + left_pages,
+				gfp_mask);
 		if (IS_ERR(s)) {
 			/*
 			 * Adjust entry length to be as before function was
 			 * called.
 			 */
-			if (prv)
-				prv->length = prv_len;
-			return s;
+			if (sgt_append->prv)
+				sgt_append->prv->length = prv_len;
+			return PTR_ERR(s);
 		}
 		chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
 		sg_set_page(s, pages[cur_page],
@@ -514,11 +537,13 @@  struct scatterlist *sg_alloc_append_table_from_pages(struct sg_table *sgt,
 		offset = 0;
 		cur_page = j;
 	}
-	sgt->nents += added_nents;
+	sgt_append->sgt.nents += added_nents;
+	sgt_append->sgt.orig_nents = sgt_append->sgt.nents;
+	sgt_append->prv = s;
 out:
 	if (!left_pages)
 		sg_mark_end(s);
-	return s;
+	return 0;
 }
 EXPORT_SYMBOL(sg_alloc_append_table_from_pages);
 
@@ -550,8 +575,18 @@  int sg_alloc_table_from_pages_segment(struct sg_table *sgt, struct page **pages,
 				unsigned long size, unsigned int max_segment,
 				gfp_t gfp_mask)
 {
-	return PTR_ERR_OR_ZERO(sg_alloc_append_table_from_pages(sgt, pages,
-			n_pages, offset, size, max_segment, NULL, 0, gfp_mask));
+	struct sg_append_table append = {};
+	int err;
+
+	err = sg_alloc_append_table_from_pages(&append, pages, n_pages, offset,
+					       size, max_segment, 0, gfp_mask);
+	if (err) {
+		sg_free_append_table(&append);
+		return err;
+	}
+	memcpy(sgt, &append.sgt, sizeof(*sgt));
+	WARN_ON(append.total_nents != sgt->orig_nents);
+	return 0;
 }
 EXPORT_SYMBOL(sg_alloc_table_from_pages_segment);
 
diff --git a/tools/testing/scatterlist/main.c b/tools/testing/scatterlist/main.c
index c2ff9179c2cc..08465a701cd5 100644
--- a/tools/testing/scatterlist/main.c
+++ b/tools/testing/scatterlist/main.c
@@ -85,43 +85,46 @@  int main(void)
 
 	for (i = 0, test = tests; test->expected_segments; test++, i++) {
 		int left_pages = test->pfn_app ? test->num_pages : 0;
+		struct sg_append_table append = {};
 		struct page *pages[MAX_PAGES];
-		struct sg_table st;
-		struct scatterlist *sg = NULL;
 		int ret;
 
 		set_pages(pages, test->pfn, test->num_pages);
 
-		if (test->pfn_app) {
-			sg = sg_alloc_append_table_from_pages(
-				&st, pages, test->num_pages, 0, test->size,
-				test->max_seg, NULL, left_pages, GFP_KERNEL);
-			assert(PTR_ERR_OR_ZERO(sg) == test->alloc_ret);
-		} else {
+		if (test->pfn_app)
+			ret = sg_alloc_append_table_from_pages(
+				&append, pages, test->num_pages, 0, test->size,
+				test->max_seg, left_pages, GFP_KERNEL);
+		else
 			ret = sg_alloc_table_from_pages_segment(
-				&st, pages, test->num_pages, 0, test->size,
-				test->max_seg, GFP_KERNEL);
-			assert(ret == test->alloc_ret);
-		}
+				&append.sgt, pages, test->num_pages, 0,
+				test->size, test->max_seg, GFP_KERNEL);
+
+		assert(ret == test->alloc_ret);
 
 		if (test->alloc_ret)
 			continue;
 
 		if (test->pfn_app) {
 			set_pages(pages, test->pfn_app, test->num_pages);
-			sg = sg_alloc_append_table_from_pages(
-				&st, pages, test->num_pages, 0, test->size,
-				test->max_seg, sg, 0, GFP_KERNEL);
+			ret = sg_alloc_append_table_from_pages(
+				&append, pages, test->num_pages, 0, test->size,
+				test->max_seg, 0, GFP_KERNEL);
 
-			assert(PTR_ERR_OR_ZERO(sg) == test->alloc_ret);
+			assert(ret == test->alloc_ret);
 		}
 
-		VALIDATE(st.nents == test->expected_segments, &st, test);
+		VALIDATE(append.sgt.nents == test->expected_segments,
+			 &append.sgt, test);
 		if (!test->pfn_app)
-			VALIDATE(st.orig_nents == test->expected_segments, &st,
-				 test);
-
-		sg_free_table(&st);
+			VALIDATE(append.sgt.orig_nents ==
+					 test->expected_segments,
+				 &append.sgt, test);
+
+		if (test->pfn_app)
+			sg_free_append_table(&append);
+		else
+			sg_free_table(&append.sgt);
 	}
 
 	assert(i == (sizeof(tests) / sizeof(tests[0])) - 1);