Re: [PATCH] dmaengine: pl330: fix descriptor allocation fail

[Vinod Koul]

On Tue, Sep 26, 2017 at 09:03:50PM +0300, Alexander Kochetkov wrote:
> Hello Vinod! Thanks for review!
> 
> > 26 сент. 2017 г., в 20:37, Vinod Koul  написал(а):
> > 
> > Tested-by please...
> 
> In order to test the patch the driver should be rebuild with NR_DEFAULT_DESC 
> defined to 1
> and with some trace code included. Is it OK if I provide second patch I used 
> for testing
> with trace showing how change work?
> 
> > one more wrapper why, we dont have any logic here!
> The idea was to keep rest of driver code intact. Ok, I’ll send v2 with no 
> wrappers.
> 
> > right justifed please
> 
> 
> Some functions has two tabs on second line, some has alignment to beginning of
> argument declaration. How correct?
> 
> 1) or like this (two tabs)
> static int add_desc(struct list_head *pool, spinlock_t *lock,
> gfp_t flg, int count)
> 
> 2) Like this:
> static int add_desc(struct list_head *pool, spinlock_t *lock,
>  gfp_t flg, int count)

Second one with one more tab :)

See Section 2  Breaking long lines and strings in
Documentation/process/coding-style.rst

-- 
~Vinod

Re: [PATCH] dmaengine: pl330: fix descriptor allocation fail

[Vinod Koul]

On Tue, Sep 26, 2017 at 09:03:50PM +0300, Alexander Kochetkov wrote:
> Hello Vinod! Thanks for review!
> 
> > 26 сент. 2017 г., в 20:37, Vinod Koul  написал(а):
> > 
> > Tested-by please...
> 
> In order to test the patch the driver should be rebuild with NR_DEFAULT_DESC 
> defined to 1
> and with some trace code included. Is it OK if I provide second patch I used 
> for testing
> with trace showing how change work?
> 
> > one more wrapper why, we dont have any logic here!
> The idea was to keep rest of driver code intact. Ok, I’ll send v2 with no 
> wrappers.
> 
> > right justifed please
> 
> 
> Some functions has two tabs on second line, some has alignment to beginning of
> argument declaration. How correct?
> 
> 1) or like this (two tabs)
> static int add_desc(struct list_head *pool, spinlock_t *lock,
> gfp_t flg, int count)
> 
> 2) Like this:
> static int add_desc(struct list_head *pool, spinlock_t *lock,
>  gfp_t flg, int count)

Second one with one more tab :)

See Section 2  Breaking long lines and strings in
Documentation/process/coding-style.rst

-- 
~Vinod

Re: [PATCH] dmaengine: pl330: fix descriptor allocation fail

[Alexander Kochetkov]

Hello Vinod! Thanks for review!

> 26 сент. 2017 г., в 20:37, Vinod Koul  написал(а):
> 
> Tested-by please...

In order to test the patch the driver should be rebuild with NR_DEFAULT_DESC 
defined to 1
and with some trace code included. Is it OK if I provide second patch I used 
for testing
with trace showing how change work?

> one more wrapper why, we dont have any logic here!
The idea was to keep rest of driver code intact. Ok, I’ll send v2 with no 
wrappers.

> right justifed please


Some functions has two tabs on second line, some has alignment to beginning of
argument declaration. How correct?

1) or like this (two tabs)
static int add_desc(struct list_head *pool, spinlock_t *lock,
gfp_t flg, int count)

2) Like this:
static int add_desc(struct list_head *pool, spinlock_t *lock,
   gfp_t flg, int count)

Regards,
Alexander.

Re: [PATCH] dmaengine: pl330: fix descriptor allocation fail

[Alexander Kochetkov]

Hello Vinod! Thanks for review!

> 26 сент. 2017 г., в 20:37, Vinod Koul  написал(а):
> 
> Tested-by please...

In order to test the patch the driver should be rebuild with NR_DEFAULT_DESC 
defined to 1
and with some trace code included. Is it OK if I provide second patch I used 
for testing
with trace showing how change work?

> one more wrapper why, we dont have any logic here!
The idea was to keep rest of driver code intact. Ok, I’ll send v2 with no 
wrappers.

> right justifed please


Some functions has two tabs on second line, some has alignment to beginning of
argument declaration. How correct?

1) or like this (two tabs)
static int add_desc(struct list_head *pool, spinlock_t *lock,
gfp_t flg, int count)

2) Like this:
static int add_desc(struct list_head *pool, spinlock_t *lock,
   gfp_t flg, int count)

Regards,
Alexander.

Re: [PATCH] dmaengine: pl330: fix descriptor allocation fail

[Vinod Koul]

On Fri, Sep 08, 2017 at 01:00:26PM +0300, Alexander Kochetkov wrote:
> Thread A calls pl330_get_desc() to get descriptor. If DMAC descriptor
> pool is empty pl330_get_desc() allocates new descriptor using add_desc()
> and then get newly allocated descriptor using pluck_desc().
> It is possible that another concurrent thread B calls pluck_desc()
> and catch newly allocated descriptor. In that case descriptor allocation
> for thread A will fail with:
> 
> kernel: dma-pl330 20078000.dma-controller: pl330_get_desc:2469 ALERT!
> 
> The commit fix the issue by calling _add_desc() to allocate new descriptor
> to the local on stack pool and than get it from local pool. So the issue
> described will nether happen.

Tested-by please...

> 
> Signed-off-by: Alexander Kochetkov 
> ---
>  drivers/dma/pl330.c |   44 +++-
>  1 file changed, 27 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index f37f497..0e7f6c9 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -2417,7 +2417,8 @@ static inline void _init_desc(struct dma_pl330_desc 
> *desc)
>  }
>  
>  /* Returns the number of descriptors added to the DMAC pool */
> -static int add_desc(struct pl330_dmac *pl330, gfp_t flg, int count)
> +static int _add_desc(struct list_head *pool, spinlock_t *lock,
> + gfp_t flg, int count)

right justifed please

>  {
>   struct dma_pl330_desc *desc;
>   unsigned long flags;
> @@ -2427,27 +2428,33 @@ static int add_desc(struct pl330_dmac *pl330, gfp_t 
> flg, int count)
>   if (!desc)
>   return 0;
>  
> - spin_lock_irqsave(>pool_lock, flags);
> + spin_lock_irqsave(lock, flags);
>  
>   for (i = 0; i < count; i++) {
>   _init_desc([i]);
> - list_add_tail([i].node, >desc_pool);
> + list_add_tail([i].node, pool);
>   }
>  
> - spin_unlock_irqrestore(>pool_lock, flags);
> + spin_unlock_irqrestore(lock, flags);
>  
>   return count;
>  }
>  
> -static struct dma_pl330_desc *pluck_desc(struct pl330_dmac *pl330)
> +static int add_desc(struct pl330_dmac *pl330, gfp_t flg, int count)
> +{
> + return _add_desc(>desc_pool, >pool_lock, flg, count);

hmmm why add a wrapper?

> +}
> +
> +static struct dma_pl330_desc *_pluck_desc(struct list_head *pool,
> + spinlock_t *lock)

here too, it helps in readability

>  {
>   struct dma_pl330_desc *desc = NULL;
>   unsigned long flags;
>  
> - spin_lock_irqsave(>pool_lock, flags);
> + spin_lock_irqsave(lock, flags);
>  
> - if (!list_empty(>desc_pool)) {
> - desc = list_entry(pl330->desc_pool.next,
> + if (!list_empty(pool)) {
> + desc = list_entry(pool->next,
>   struct dma_pl330_desc, node);
>  
>   list_del_init(>node);
> @@ -2456,11 +2463,16 @@ static struct dma_pl330_desc *pluck_desc(struct 
> pl330_dmac *pl330)
>   desc->txd.callback = NULL;
>   }
>  
> - spin_unlock_irqrestore(>pool_lock, flags);
> + spin_unlock_irqrestore(lock, flags);
>  
>   return desc;
>  }
>  
> +static struct dma_pl330_desc *pluck_desc(struct pl330_dmac *pl330)
> +{
> + return _pluck_desc(>desc_pool, >pool_lock);

one more wrapper why, we dont have any logic here!

> +}
> +
>  static struct dma_pl330_desc *pl330_get_desc(struct dma_pl330_chan *pch)
>  {
>   struct pl330_dmac *pl330 = pch->dmac;
> @@ -2472,16 +2484,14 @@ static struct dma_pl330_desc *pl330_get_desc(struct 
> dma_pl330_chan *pch)
>  
>   /* If the DMAC pool is empty, alloc new */
>   if (!desc) {
> - if (!add_desc(pl330, GFP_ATOMIC, 1))
> - return NULL;
> + DEFINE_SPINLOCK(lock);
> + LIST_HEAD(pool);
>  
> - /* Try again */
> - desc = pluck_desc(pl330);
> - if (!desc) {
> - dev_err(pch->dmac->ddma.dev,
> - "%s:%d ALERT!\n", __func__, __LINE__);
> + if (!_add_desc(, , GFP_ATOMIC, 1))
>   return NULL;
> - }
> +
> + desc = _pluck_desc(, );
> + WARN_ON(!desc || !list_empty());
>   }
>  
>   /* Initialize the descriptor */
> -- 
> 1.7.9.5
> 

-- 
~Vinod

Re: [PATCH] dmaengine: pl330: fix descriptor allocation fail

[Vinod Koul]

On Fri, Sep 08, 2017 at 01:00:26PM +0300, Alexander Kochetkov wrote:
> Thread A calls pl330_get_desc() to get descriptor. If DMAC descriptor
> pool is empty pl330_get_desc() allocates new descriptor using add_desc()
> and then get newly allocated descriptor using pluck_desc().
> It is possible that another concurrent thread B calls pluck_desc()
> and catch newly allocated descriptor. In that case descriptor allocation
> for thread A will fail with:
> 
> kernel: dma-pl330 20078000.dma-controller: pl330_get_desc:2469 ALERT!
> 
> The commit fix the issue by calling _add_desc() to allocate new descriptor
> to the local on stack pool and than get it from local pool. So the issue
> described will nether happen.

Tested-by please...

> 
> Signed-off-by: Alexander Kochetkov 
> ---
>  drivers/dma/pl330.c |   44 +++-
>  1 file changed, 27 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index f37f497..0e7f6c9 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -2417,7 +2417,8 @@ static inline void _init_desc(struct dma_pl330_desc 
> *desc)
>  }
>  
>  /* Returns the number of descriptors added to the DMAC pool */
> -static int add_desc(struct pl330_dmac *pl330, gfp_t flg, int count)
> +static int _add_desc(struct list_head *pool, spinlock_t *lock,
> + gfp_t flg, int count)

right justifed please

>  {
>   struct dma_pl330_desc *desc;
>   unsigned long flags;
> @@ -2427,27 +2428,33 @@ static int add_desc(struct pl330_dmac *pl330, gfp_t 
> flg, int count)
>   if (!desc)
>   return 0;
>  
> - spin_lock_irqsave(>pool_lock, flags);
> + spin_lock_irqsave(lock, flags);
>  
>   for (i = 0; i < count; i++) {
>   _init_desc([i]);
> - list_add_tail([i].node, >desc_pool);
> + list_add_tail([i].node, pool);
>   }
>  
> - spin_unlock_irqrestore(>pool_lock, flags);
> + spin_unlock_irqrestore(lock, flags);
>  
>   return count;
>  }
>  
> -static struct dma_pl330_desc *pluck_desc(struct pl330_dmac *pl330)
> +static int add_desc(struct pl330_dmac *pl330, gfp_t flg, int count)
> +{
> + return _add_desc(>desc_pool, >pool_lock, flg, count);

hmmm why add a wrapper?

> +}
> +
> +static struct dma_pl330_desc *_pluck_desc(struct list_head *pool,
> + spinlock_t *lock)

here too, it helps in readability

>  {
>   struct dma_pl330_desc *desc = NULL;
>   unsigned long flags;
>  
> - spin_lock_irqsave(>pool_lock, flags);
> + spin_lock_irqsave(lock, flags);
>  
> - if (!list_empty(>desc_pool)) {
> - desc = list_entry(pl330->desc_pool.next,
> + if (!list_empty(pool)) {
> + desc = list_entry(pool->next,
>   struct dma_pl330_desc, node);
>  
>   list_del_init(>node);
> @@ -2456,11 +2463,16 @@ static struct dma_pl330_desc *pluck_desc(struct 
> pl330_dmac *pl330)
>   desc->txd.callback = NULL;
>   }
>  
> - spin_unlock_irqrestore(>pool_lock, flags);
> + spin_unlock_irqrestore(lock, flags);
>  
>   return desc;
>  }
>  
> +static struct dma_pl330_desc *pluck_desc(struct pl330_dmac *pl330)
> +{
> + return _pluck_desc(>desc_pool, >pool_lock);

one more wrapper why, we dont have any logic here!

> +}
> +
>  static struct dma_pl330_desc *pl330_get_desc(struct dma_pl330_chan *pch)
>  {
>   struct pl330_dmac *pl330 = pch->dmac;
> @@ -2472,16 +2484,14 @@ static struct dma_pl330_desc *pl330_get_desc(struct 
> dma_pl330_chan *pch)
>  
>   /* If the DMAC pool is empty, alloc new */
>   if (!desc) {
> - if (!add_desc(pl330, GFP_ATOMIC, 1))
> - return NULL;
> + DEFINE_SPINLOCK(lock);
> + LIST_HEAD(pool);
>  
> - /* Try again */
> - desc = pluck_desc(pl330);
> - if (!desc) {
> - dev_err(pch->dmac->ddma.dev,
> - "%s:%d ALERT!\n", __func__, __LINE__);
> + if (!_add_desc(, , GFP_ATOMIC, 1))
>   return NULL;
> - }
> +
> + desc = _pluck_desc(, );
> + WARN_ON(!desc || !list_empty());
>   }
>  
>   /* Initialize the descriptor */
> -- 
> 1.7.9.5
> 

-- 
~Vinod