linux-kernel - Re: [PATCH V4 2/2] ptr_ring: try vmalloc() when kmalloc() fails

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Date:   Fri, 9 Feb 2018 17:53:50 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH V4 2/2] ptr_ring: try vmalloc() when kmalloc() fails

On Fri, Feb 09, 2018 at 05:45:50PM +0800, Jason Wang wrote:
> This patch switch to use kvmalloc_array() for using a vmalloc()
> fallback to help in case kmalloc() fails.

Above isn't really saying anything about the motivation, it
just explains what kvmalloc_array does.

How about:

Switch ptr_ring from kmalloc to kvmalloc. This way it can support larger
ring sizes.

> 
> Reported-by: syzbot+e4d4f9ddd4295539735d@...kaller.appspotmail.com
> Fixes: 2e0ab8ca83c12 ("ptr_ring: array based FIFO for pointers")

I don't see this as a bugfix - it's more of an enhancement.

Do we need this in net or can we defer this to net-next?

I'm not sure myself. For now

Acked-by: Michael S. Tsirkin <mst@...hat.com>

> Signed-off-by: Jason Wang <jasowang@...hat.com>


> ---
>  include/linux/ptr_ring.h | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 6051a5f..b884b77 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -464,11 +464,14 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
>  	__PTR_RING_PEEK_CALL_v; \
>  })
>  
> +/* Not all gfp_t flags (besides GFP_KERNEL) are allowed. See
> + * documentation for vmalloc for which of them are legal.
> + */
>  static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
>  {
>  	if (size * sizeof(void *) > KMALLOC_MAX_SIZE)
>  		return NULL;
> -	return kcalloc(size, sizeof(void *), gfp);
> +	return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO);
>  }
>  
>  static inline void __ptr_ring_set_size(struct ptr_ring *r, int size)
> @@ -603,7 +606,7 @@ static inline int ptr_ring_resize(struct ptr_ring *r, int size, gfp_t gfp,
>  	spin_unlock(&(r)->producer_lock);
>  	spin_unlock_irqrestore(&(r)->consumer_lock, flags);
>  
> -	kfree(old);
> +	kvfree(old);
>  
>  	return 0;
>  }
> @@ -643,7 +646,7 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings,
>  	}
>  
>  	for (i = 0; i < nrings; ++i)
> -		kfree(queues[i]);
> +		kvfree(queues[i]);
>  
>  	kfree(queues);
>  
> @@ -651,7 +654,7 @@ static inline int ptr_ring_resize_multiple(struct ptr_ring **rings,
>  
>  nomem:
>  	while (--i >= 0)
> -		kfree(queues[i]);
> +		kvfree(queues[i]);
>  
>  	kfree(queues);
>  
> @@ -666,7 +669,7 @@ static inline void ptr_ring_cleanup(struct ptr_ring *r, void (*destroy)(void *))
>  	if (destroy)
>  		while ((ptr = ptr_ring_consume(r)))
>  			destroy(ptr);
> -	kfree(r->queue);
> +	kvfree(r->queue);
>  }
>  
>  #endif /* _LINUX_PTR_RING_H  */
> -- 
> 2.7.4