Re: [PATCH v4] dma-buf: fix racing conflict of dma_heap_add()

[Christian König]

Hi Dawei,

from the technical description, coding style etc.. it looks clean to me, 
but I'm the completely wrong person to ask for a background check.

I have a high level understanding of how dma-heaps work, but not a 
single line of this code is from me.

Feel free to add my Acked-by, but Laura, John and others do you have any 
opinion?

Regards,
Christian.

Am 21.11.22 um 16:28 schrieb Dawei Li:
> On Sat, Nov 05, 2022 at 12:05:36AM +0800, Dawei Li wrote:
>
> Hi Christian,
> May I have your opinion on this change?
>
> Thanks,
> Dawei
>
> > Racing conflict could be:
> > task A                 task B
> > list_for_each_entry
> > strcmp(h->name))
> >                         list_for_each_entry
> >                         strcmp(h->name)
> > kzalloc                kzalloc
> > ......                 .....
> > device_create          device_create
> > list_add
> >                         list_add
> >
> > The root cause is that task B has no idea about the fact someone
> > else(A) has inserted heap with same name when it calls list_add,
> > so a potential collision occurs.
> >
> > Fixes: c02a81fba74f ("dma-buf: Add dma-buf heaps framework")
> > Signed-off-by: Dawei Li <set_pte_at@xxxxxxxxxxx>
> > ---
> > v1: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2FTYCP286MB2323950197F60FC3473123B7CA349%40TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM%2F&amp;data=05%7C01%7Cchristian.koenig%40amd.com%7C1989f31257fc458a27c508dacbd5078e%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638046413707443203%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=OWPUPrIHGnzwXyQE4WlIthThwSuSK2y3Eq2Wq5zAzbo%3D&amp;reserved=0
> > v1->v2: Narrow down locking scope, check the existence of heap before
> > insertion, as suggested by Andrew Davis.
> > v2->v3: Remove double checking.
> > v3->v4: Minor coding style and patch formatting adjustment.
> > ---
> >   drivers/dma-buf/dma-heap.c | 28 +++++++++++++++-------------
> >   1 file changed, 15 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> > index 8f5848aa144f..59d158873f4c 100644
> > --- a/drivers/dma-buf/dma-heap.c
> > +++ b/drivers/dma-buf/dma-heap.c
> > @@ -233,18 +233,6 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
> >   		return ERR_PTR(-EINVAL);
> >   	}
> >   
> > -	/* check the name is unique */
> > -	mutex_lock(&heap_list_lock);
> > -	list_for_each_entry(h, &heap_list, list) {
> > -		if (!strcmp(h->name, exp_info->name)) {
> > -			mutex_unlock(&heap_list_lock);
> > -			pr_err("dma_heap: Already registered heap named %s\n",
> > -			       exp_info->name);
> > -			return ERR_PTR(-EINVAL);
> > -		}
> > -	}
> > -	mutex_unlock(&heap_list_lock);
> > -
> >   	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
> >   	if (!heap)
> >   		return ERR_PTR(-ENOMEM);
> > @@ -283,13 +271,27 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
> >   		err_ret = ERR_CAST(dev_ret);
> >   		goto err2;
> >   	}
> > -	/* Add heap to the list */
> > +
> >   	mutex_lock(&heap_list_lock);
> > +	/* check the name is unique */
> > +	list_for_each_entry(h, &heap_list, list) {
> > +		if (!strcmp(h->name, exp_info->name)) {
> > +			mutex_unlock(&heap_list_lock);
> > +			pr_err("dma_heap: Already registered heap named %s\n",
> > +			       exp_info->name);
> > +			err_ret = ERR_PTR(-EINVAL);
> > +			goto err3;
> > +		}
> > +	}
> > +
> > +	/* Add heap to the list */
> >   	list_add(&heap->list, &heap_list);
> >   	mutex_unlock(&heap_list_lock);
> >   
> >   	return heap;
> >   
> > +err3:
> > +	device_destroy(dma_heap_class, heap->heap_devt);
> >   err2:
> >   	cdev_del(&heap->heap_cdev);
> >   err1:
> > --
> > 2.25.1