Re: [PATCH v2] async_pq: Remove VLA usage

2018-05-30 Thread Dan Williams 
On Wed, May 30, 2018 at 2:33 PM, Kees Cook  wrote:
> On Tue, May 29, 2018 at 3:40 PM, Dan Williams  
> wrote:
>> [ add Vinod's korg address ]
>>
>> On Tue, May 29, 2018 at 3:37 PM, Dan Williams  
>> wrote:
>>> [ adding linux-raid ]
>>>
>>> Apologies for the delay, the recent ping from Kees made me take a closer 
>>> look.
>>>
>>> On Sat, May 5, 2018 at 12:58 AM, Kyle Spiers  wrote:
 In the quest to remove VLAs from the kernel[1], this moves the
 allocation of coefs and blocks from the stack to being kmalloc()ed.

 [1] https://lkml.org/lkml/2018/3/7/621

 Signed-off-by: Kyle Spiers 
 ---
 Forgot to add slab.h
 ---
  crypto/async_tx/async_pq.c  | 18 ++
  crypto/async_tx/raid6test.c |  9 -
  2 files changed, 22 insertions(+), 5 deletions(-)

 diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
 index 56bd612927ab..af1912313a23 100644
 --- a/crypto/async_tx/async_pq.c
 +++ b/crypto/async_tx/async_pq.c
 @@ -194,9 +194,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
 offset, int disks,
 (src_cnt <= dma_maxpq(device, 0) ||
  dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
 is_dma_pq_aligned(device, offset, 0, len)) {
 -   struct dma_async_tx_descriptor *tx;
 +   struct dma_async_tx_descriptor *tx = NULL;
 enum dma_ctrl_flags dma_flags = 0;
 -   unsigned char coefs[src_cnt];
 +   unsigned char *coefs;
>>> At a minimum this needs to be GFP_NOIO since raid may be in the
>>> page-reclaim path.
>>>
>>> However, I think it may be better to allocate this with the rest of
>>> the stripe resources and pass it in as a scratch buffer. See the usage
>>> / implementation of scribble_alloc() in drivers/md/raid5.c.
>
> Given this:
>
> int src_cnt = disks - 2;
> ...
> BUG_ON(disks > 255 || ...)
>
> what about just making something like:
>
> #define MAX_DISKS 255
> ...
> int src_cnt = disks - 2;
> ...
> BUG_ON(disks > MAX_DISKS || ...)
> ...
>  unsigned char coefs[MAX_DISKS];
>
> ?

Yeah, we were already potentially suffering a value that large on the
stack in a max config case anyway with the VLA. Looks ok to me.

Re: [PATCH v2] async_pq: Remove VLA usage

2018-05-30 Thread Dan Williams 
On Wed, May 30, 2018 at 2:33 PM, Kees Cook  wrote:
> On Tue, May 29, 2018 at 3:40 PM, Dan Williams  
> wrote:
>> [ add Vinod's korg address ]
>>
>> On Tue, May 29, 2018 at 3:37 PM, Dan Williams  
>> wrote:
>>> [ adding linux-raid ]
>>>
>>> Apologies for the delay, the recent ping from Kees made me take a closer 
>>> look.
>>>
>>> On Sat, May 5, 2018 at 12:58 AM, Kyle Spiers  wrote:
 In the quest to remove VLAs from the kernel[1], this moves the
 allocation of coefs and blocks from the stack to being kmalloc()ed.

 [1] https://lkml.org/lkml/2018/3/7/621

 Signed-off-by: Kyle Spiers 
 ---
 Forgot to add slab.h
 ---
  crypto/async_tx/async_pq.c  | 18 ++
  crypto/async_tx/raid6test.c |  9 -
  2 files changed, 22 insertions(+), 5 deletions(-)

 diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
 index 56bd612927ab..af1912313a23 100644
 --- a/crypto/async_tx/async_pq.c
 +++ b/crypto/async_tx/async_pq.c
 @@ -194,9 +194,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
 offset, int disks,
 (src_cnt <= dma_maxpq(device, 0) ||
  dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
 is_dma_pq_aligned(device, offset, 0, len)) {
 -   struct dma_async_tx_descriptor *tx;
 +   struct dma_async_tx_descriptor *tx = NULL;
 enum dma_ctrl_flags dma_flags = 0;
 -   unsigned char coefs[src_cnt];
 +   unsigned char *coefs;
>>> At a minimum this needs to be GFP_NOIO since raid may be in the
>>> page-reclaim path.
>>>
>>> However, I think it may be better to allocate this with the rest of
>>> the stripe resources and pass it in as a scratch buffer. See the usage
>>> / implementation of scribble_alloc() in drivers/md/raid5.c.
>
> Given this:
>
> int src_cnt = disks - 2;
> ...
> BUG_ON(disks > 255 || ...)
>
> what about just making something like:
>
> #define MAX_DISKS 255
> ...
> int src_cnt = disks - 2;
> ...
> BUG_ON(disks > MAX_DISKS || ...)
> ...
>  unsigned char coefs[MAX_DISKS];
>
> ?

Yeah, we were already potentially suffering a value that large on the
stack in a max config case anyway with the VLA. Looks ok to me.

Re: [PATCH v2] async_pq: Remove VLA usage

2018-05-10 Thread Kees Cook 
On Sat, May 5, 2018 at 12:58 AM, Kyle Spiers  wrote:
> In the quest to remove VLAs from the kernel[1], this moves the
> allocation of coefs and blocks from the stack to being kmalloc()ed.
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Kyle Spiers 

Reviewed-by: Kees Cook 

Is this something that should go via Vinod, Dan, or direct through
Herbert's crypto tree?

Thanks!

-Kees

> ---
> Forgot to add slab.h
> ---
>  crypto/async_tx/async_pq.c  | 18 ++
>  crypto/async_tx/raid6test.c |  9 -
>  2 files changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
> index 56bd612927ab..af1912313a23 100644
> --- a/crypto/async_tx/async_pq.c
> +++ b/crypto/async_tx/async_pq.c
> @@ -194,9 +194,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
> offset, int disks,
> (src_cnt <= dma_maxpq(device, 0) ||
>  dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
> is_dma_pq_aligned(device, offset, 0, len)) {
> -   struct dma_async_tx_descriptor *tx;
> +   struct dma_async_tx_descriptor *tx = NULL;
> enum dma_ctrl_flags dma_flags = 0;
> -   unsigned char coefs[src_cnt];
> +   unsigned char *coefs;
> int i, j;
>
> /* run the p+q asynchronously */
> @@ -207,6 +207,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
> offset, int disks,
>  * sources and update the coefficients accordingly
>  */
> unmap->len = len;
> +   coefs = kmalloc_array(src_cnt, sizeof(*coefs), GFP_KERNEL);
> +   if (!coefs)
> +   goto out;
> for (i = 0, j = 0; i < src_cnt; i++) {
> if (blocks[i] == NULL)
> continue;
> @@ -240,7 +243,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
> offset, int disks,
> }
>
> tx = do_async_gen_syndrome(chan, coefs, j, unmap, dma_flags, 
> submit);
> +out:
> dmaengine_unmap_put(unmap);
> +   kfree(coefs);
> return tx;
> }
>
> @@ -298,8 +303,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
> offset, int disks,
>  {
> struct dma_chan *chan = pq_val_chan(submit, blocks, disks, len);
> struct dma_device *device = chan ? chan->device : NULL;
> -   struct dma_async_tx_descriptor *tx;
> -   unsigned char coefs[disks-2];
> +   struct dma_async_tx_descriptor *tx = NULL;
> +   unsigned char *coefs = NULL;
> enum dma_ctrl_flags dma_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 
> 0;
> struct dmaengine_unmap_data *unmap = NULL;
>
> @@ -318,6 +323,9 @@ async_syndrome_val(struct page **blocks, unsigned int 
> offset, int disks,
>  __func__, disks, len);
>
> unmap->len = len;
> +   coefs = kmalloc_array(disks - 2, sizeof(*coefs), GFP_KERNEL);
> +   if (!coefs)
> +   goto out;
> for (i = 0; i < disks-2; i++)
> if (likely(blocks[i])) {
> unmap->addr[j] = dma_map_page(dev, blocks[i],
> @@ -423,6 +431,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
> offset, int disks,
> async_tx_sync_epilog(submit);
> tx = NULL;
> }
> +out:
> +   kfree(coefs);
> dmaengine_unmap_put(unmap);
>
> return tx;
> diff --git a/crypto/async_tx/raid6test.c b/crypto/async_tx/raid6test.c
> index dad95f45b88f..4237a5ae8f42 100644
> --- a/crypto/async_tx/raid6test.c
> +++ b/crypto/async_tx/raid6test.c
> @@ -24,6 +24,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>
>  #undef pr
>  #define pr(fmt, args...) pr_info("raid6test: " fmt, ##args)
> @@ -81,11 +82,16 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
> faila, int failb, stru
> init_async_submit(, 0, NULL, NULL, NULL, 
> addr_conv);
> tx = async_gen_syndrome(ptrs, 0, disks, bytes, 
> );
> } else {
> -   struct page *blocks[disks];
> +   struct page **blocks;
> struct page *dest;
> int count = 0;
> int i;
>
> +   blocks = kmalloc_array(disks, sizeof(*blocks),
> +   GFP_KERNEL);
> +   if (!blocks)
> +   return;
> +
> /* data+Q failure.  Reconstruct data from P,
>  * then rebuild syndrome
>  */
> @@ -101,6 +107,7 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
> faila, int failb, stru
>
>

Re: [PATCH v2] async_pq: Remove VLA usage

2018-05-10 Thread Kees Cook 
On Sat, May 5, 2018 at 12:58 AM, Kyle Spiers  wrote:
> In the quest to remove VLAs from the kernel[1], this moves the
> allocation of coefs and blocks from the stack to being kmalloc()ed.
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Kyle Spiers 

Reviewed-by: Kees Cook 

Is this something that should go via Vinod, Dan, or direct through
Herbert's crypto tree?

Thanks!

-Kees

> ---
> Forgot to add slab.h
> ---
>  crypto/async_tx/async_pq.c  | 18 ++
>  crypto/async_tx/raid6test.c |  9 -
>  2 files changed, 22 insertions(+), 5 deletions(-)
>
> diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
> index 56bd612927ab..af1912313a23 100644
> --- a/crypto/async_tx/async_pq.c
> +++ b/crypto/async_tx/async_pq.c
> @@ -194,9 +194,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
> offset, int disks,
> (src_cnt <= dma_maxpq(device, 0) ||
>  dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
> is_dma_pq_aligned(device, offset, 0, len)) {
> -   struct dma_async_tx_descriptor *tx;
> +   struct dma_async_tx_descriptor *tx = NULL;
> enum dma_ctrl_flags dma_flags = 0;
> -   unsigned char coefs[src_cnt];
> +   unsigned char *coefs;
> int i, j;
>
> /* run the p+q asynchronously */
> @@ -207,6 +207,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
> offset, int disks,
>  * sources and update the coefficients accordingly
>  */
> unmap->len = len;
> +   coefs = kmalloc_array(src_cnt, sizeof(*coefs), GFP_KERNEL);
> +   if (!coefs)
> +   goto out;
> for (i = 0, j = 0; i < src_cnt; i++) {
> if (blocks[i] == NULL)
> continue;
> @@ -240,7 +243,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
> offset, int disks,
> }
>
> tx = do_async_gen_syndrome(chan, coefs, j, unmap, dma_flags, 
> submit);
> +out:
> dmaengine_unmap_put(unmap);
> +   kfree(coefs);
> return tx;
> }
>
> @@ -298,8 +303,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
> offset, int disks,
>  {
> struct dma_chan *chan = pq_val_chan(submit, blocks, disks, len);
> struct dma_device *device = chan ? chan->device : NULL;
> -   struct dma_async_tx_descriptor *tx;
> -   unsigned char coefs[disks-2];
> +   struct dma_async_tx_descriptor *tx = NULL;
> +   unsigned char *coefs = NULL;
> enum dma_ctrl_flags dma_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 
> 0;
> struct dmaengine_unmap_data *unmap = NULL;
>
> @@ -318,6 +323,9 @@ async_syndrome_val(struct page **blocks, unsigned int 
> offset, int disks,
>  __func__, disks, len);
>
> unmap->len = len;
> +   coefs = kmalloc_array(disks - 2, sizeof(*coefs), GFP_KERNEL);
> +   if (!coefs)
> +   goto out;
> for (i = 0; i < disks-2; i++)
> if (likely(blocks[i])) {
> unmap->addr[j] = dma_map_page(dev, blocks[i],
> @@ -423,6 +431,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
> offset, int disks,
> async_tx_sync_epilog(submit);
> tx = NULL;
> }
> +out:
> +   kfree(coefs);
> dmaengine_unmap_put(unmap);
>
> return tx;
> diff --git a/crypto/async_tx/raid6test.c b/crypto/async_tx/raid6test.c
> index dad95f45b88f..4237a5ae8f42 100644
> --- a/crypto/async_tx/raid6test.c
> +++ b/crypto/async_tx/raid6test.c
> @@ -24,6 +24,7 @@
>  #include 
>  #include 
>  #include 
> +#include 
>
>  #undef pr
>  #define pr(fmt, args...) pr_info("raid6test: " fmt, ##args)
> @@ -81,11 +82,16 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
> faila, int failb, stru
> init_async_submit(, 0, NULL, NULL, NULL, 
> addr_conv);
> tx = async_gen_syndrome(ptrs, 0, disks, bytes, 
> );
> } else {
> -   struct page *blocks[disks];
> +   struct page **blocks;
> struct page *dest;
> int count = 0;
> int i;
>
> +   blocks = kmalloc_array(disks, sizeof(*blocks),
> +   GFP_KERNEL);
> +   if (!blocks)
> +   return;
> +
> /* data+Q failure.  Reconstruct data from P,
>  * then rebuild syndrome
>  */
> @@ -101,6 +107,7 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
> faila, int failb, stru
>
> init_async_submit(, 0, tx, NULL, NULL, 
>

[PATCH v2] async_pq: Remove VLA usage

2018-05-05 Thread Kyle Spiers 
In the quest to remove VLAs from the kernel[1], this moves the
allocation of coefs and blocks from the stack to being kmalloc()ed.

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Kyle Spiers 
---
Forgot to add slab.h
---
 crypto/async_tx/async_pq.c  | 18 ++
 crypto/async_tx/raid6test.c |  9 -
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
index 56bd612927ab..af1912313a23 100644
--- a/crypto/async_tx/async_pq.c
+++ b/crypto/async_tx/async_pq.c
@@ -194,9 +194,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
offset, int disks,
(src_cnt <= dma_maxpq(device, 0) ||
 dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
is_dma_pq_aligned(device, offset, 0, len)) {
-   struct dma_async_tx_descriptor *tx;
+   struct dma_async_tx_descriptor *tx = NULL;
enum dma_ctrl_flags dma_flags = 0;
-   unsigned char coefs[src_cnt];
+   unsigned char *coefs;
int i, j;
 
/* run the p+q asynchronously */
@@ -207,6 +207,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
offset, int disks,
 * sources and update the coefficients accordingly
 */
unmap->len = len;
+   coefs = kmalloc_array(src_cnt, sizeof(*coefs), GFP_KERNEL);
+   if (!coefs)
+   goto out;
for (i = 0, j = 0; i < src_cnt; i++) {
if (blocks[i] == NULL)
continue;
@@ -240,7 +243,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
offset, int disks,
}
 
tx = do_async_gen_syndrome(chan, coefs, j, unmap, dma_flags, 
submit);
+out:
dmaengine_unmap_put(unmap);
+   kfree(coefs);
return tx;
}
 
@@ -298,8 +303,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
offset, int disks,
 {
struct dma_chan *chan = pq_val_chan(submit, blocks, disks, len);
struct dma_device *device = chan ? chan->device : NULL;
-   struct dma_async_tx_descriptor *tx;
-   unsigned char coefs[disks-2];
+   struct dma_async_tx_descriptor *tx = NULL;
+   unsigned char *coefs = NULL;
enum dma_ctrl_flags dma_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
struct dmaengine_unmap_data *unmap = NULL;
 
@@ -318,6 +323,9 @@ async_syndrome_val(struct page **blocks, unsigned int 
offset, int disks,
 __func__, disks, len);
 
unmap->len = len;
+   coefs = kmalloc_array(disks - 2, sizeof(*coefs), GFP_KERNEL);
+   if (!coefs)
+   goto out;
for (i = 0; i < disks-2; i++)
if (likely(blocks[i])) {
unmap->addr[j] = dma_map_page(dev, blocks[i],
@@ -423,6 +431,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
offset, int disks,
async_tx_sync_epilog(submit);
tx = NULL;
}
+out:
+   kfree(coefs);
dmaengine_unmap_put(unmap);
 
return tx;
diff --git a/crypto/async_tx/raid6test.c b/crypto/async_tx/raid6test.c
index dad95f45b88f..4237a5ae8f42 100644
--- a/crypto/async_tx/raid6test.c
+++ b/crypto/async_tx/raid6test.c
@@ -24,6 +24,7 @@
 #include 
 #include 
 #include 
+#include 
 
 #undef pr
 #define pr(fmt, args...) pr_info("raid6test: " fmt, ##args)
@@ -81,11 +82,16 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
faila, int failb, stru
init_async_submit(, 0, NULL, NULL, NULL, 
addr_conv);
tx = async_gen_syndrome(ptrs, 0, disks, bytes, );
} else {
-   struct page *blocks[disks];
+   struct page **blocks;
struct page *dest;
int count = 0;
int i;
 
+   blocks = kmalloc_array(disks, sizeof(*blocks),
+   GFP_KERNEL);
+   if (!blocks)
+   return;
+
/* data+Q failure.  Reconstruct data from P,
 * then rebuild syndrome
 */
@@ -101,6 +107,7 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
faila, int failb, stru
 
init_async_submit(, 0, tx, NULL, NULL, 
addr_conv);
tx = async_gen_syndrome(ptrs, 0, disks, bytes, );
+   kfree(blocks);
}
} else {
if (failb == disks-2) {
-- 
2.17.0.441.gb46fe60e1d-goog

[PATCH v2] async_pq: Remove VLA usage

2018-05-05 Thread Kyle Spiers 
In the quest to remove VLAs from the kernel[1], this moves the
allocation of coefs and blocks from the stack to being kmalloc()ed.

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Kyle Spiers 
---
Forgot to add slab.h
---
 crypto/async_tx/async_pq.c  | 18 ++
 crypto/async_tx/raid6test.c |  9 -
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
index 56bd612927ab..af1912313a23 100644
--- a/crypto/async_tx/async_pq.c
+++ b/crypto/async_tx/async_pq.c
@@ -194,9 +194,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
offset, int disks,
(src_cnt <= dma_maxpq(device, 0) ||
 dma_maxpq(device, DMA_PREP_CONTINUE) > 0) &&
is_dma_pq_aligned(device, offset, 0, len)) {
-   struct dma_async_tx_descriptor *tx;
+   struct dma_async_tx_descriptor *tx = NULL;
enum dma_ctrl_flags dma_flags = 0;
-   unsigned char coefs[src_cnt];
+   unsigned char *coefs;
int i, j;
 
/* run the p+q asynchronously */
@@ -207,6 +207,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
offset, int disks,
 * sources and update the coefficients accordingly
 */
unmap->len = len;
+   coefs = kmalloc_array(src_cnt, sizeof(*coefs), GFP_KERNEL);
+   if (!coefs)
+   goto out;
for (i = 0, j = 0; i < src_cnt; i++) {
if (blocks[i] == NULL)
continue;
@@ -240,7 +243,9 @@ async_gen_syndrome(struct page **blocks, unsigned int 
offset, int disks,
}
 
tx = do_async_gen_syndrome(chan, coefs, j, unmap, dma_flags, 
submit);
+out:
dmaengine_unmap_put(unmap);
+   kfree(coefs);
return tx;
}
 
@@ -298,8 +303,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
offset, int disks,
 {
struct dma_chan *chan = pq_val_chan(submit, blocks, disks, len);
struct dma_device *device = chan ? chan->device : NULL;
-   struct dma_async_tx_descriptor *tx;
-   unsigned char coefs[disks-2];
+   struct dma_async_tx_descriptor *tx = NULL;
+   unsigned char *coefs = NULL;
enum dma_ctrl_flags dma_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
struct dmaengine_unmap_data *unmap = NULL;
 
@@ -318,6 +323,9 @@ async_syndrome_val(struct page **blocks, unsigned int 
offset, int disks,
 __func__, disks, len);
 
unmap->len = len;
+   coefs = kmalloc_array(disks - 2, sizeof(*coefs), GFP_KERNEL);
+   if (!coefs)
+   goto out;
for (i = 0; i < disks-2; i++)
if (likely(blocks[i])) {
unmap->addr[j] = dma_map_page(dev, blocks[i],
@@ -423,6 +431,8 @@ async_syndrome_val(struct page **blocks, unsigned int 
offset, int disks,
async_tx_sync_epilog(submit);
tx = NULL;
}
+out:
+   kfree(coefs);
dmaengine_unmap_put(unmap);
 
return tx;
diff --git a/crypto/async_tx/raid6test.c b/crypto/async_tx/raid6test.c
index dad95f45b88f..4237a5ae8f42 100644
--- a/crypto/async_tx/raid6test.c
+++ b/crypto/async_tx/raid6test.c
@@ -24,6 +24,7 @@
 #include 
 #include 
 #include 
+#include 
 
 #undef pr
 #define pr(fmt, args...) pr_info("raid6test: " fmt, ##args)
@@ -81,11 +82,16 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
faila, int failb, stru
init_async_submit(, 0, NULL, NULL, NULL, 
addr_conv);
tx = async_gen_syndrome(ptrs, 0, disks, bytes, );
} else {
-   struct page *blocks[disks];
+   struct page **blocks;
struct page *dest;
int count = 0;
int i;
 
+   blocks = kmalloc_array(disks, sizeof(*blocks),
+   GFP_KERNEL);
+   if (!blocks)
+   return;
+
/* data+Q failure.  Reconstruct data from P,
 * then rebuild syndrome
 */
@@ -101,6 +107,7 @@ static void raid6_dual_recov(int disks, size_t bytes, int 
faila, int failb, stru
 
init_async_submit(, 0, tx, NULL, NULL, 
addr_conv);
tx = async_gen_syndrome(ptrs, 0, disks, bytes, );
+   kfree(blocks);
}
} else {
if (failb == disks-2) {
-- 
2.17.0.441.gb46fe60e1d-goog