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Message-ID: <CABdmKX0iR-YAfR+rLczPDa5W9Y+JMYs5RKMK8bkjs3z80TgL6A@mail.gmail.com>
Date: Tue, 1 Nov 2022 17:05:28 -0700
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Dawei Li <set_pte_at@...look.com>
Cc: sumit.semwal@...aro.org, christian.koenig@....com,
benjamin.gaignard@...labora.com, labbott@...hat.com,
Brian.Starkey@....com, jstultz@...gle.com, afd@...com,
sspatil@...roid.com, linux-media@...r.kernel.org,
dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dma-buf: fix racing conflict of dma_heap_add()
On Mon, Oct 31, 2022 at 7:53 AM Dawei Li <set_pte_at@...look.com> wrote:
>
> 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.
>
> v1: https://lore.kernel.org/all/TYCP286MB2323950197F60FC3473123B7CA349@TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM/
>
> v1->v2: Narrow down locking scope, check the existence of heap before
> insertion, as suggested by Andrew Davis.
>
> Fixes: c02a81fba74f ("dma-buf: Add dma-buf heaps framework")
>
> base-commit: 447fb14bf07905b880c9ed1ea92c53d6dd0649d7
>
> Signed-off-by: Dawei Li <set_pte_at@...look.com>
> ---
> drivers/dma-buf/dma-heap.c | 37 ++++++++++++++++++++++++++++---------
> 1 file changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index 8f5848aa144f..1c787a147e3a 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -216,9 +216,21 @@ const char *dma_heap_get_name(struct dma_heap *heap)
> return heap->name;
> }
>
> +static inline bool dma_heap_exist(const char *name)
> +{
> + struct dma_heap *h;
> +
> + list_for_each_entry(h, &heap_list, list) {
> + if (!strcmp(h->name, name))
> + return true;
> + }
> +
> + return false;
> +}
> +
> struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
> {
> - struct dma_heap *heap, *h, *err_ret;
> + struct dma_heap *heap, *err_ret;
> struct device *dev_ret;
> unsigned int minor;
> int ret;
> @@ -235,13 +247,11 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>
> /* 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);
> - }
> + if (dma_heap_exist(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);
Hi Dawei,
What Andrew was suggesting was that you entirely move the check from
here to the critical section down below, not duplicate the check. I
don't think we want to check this twice. We should be able to do this
by taking the heap_list_lock only once.
> }
> mutex_unlock(&heap_list_lock);
>
> @@ -283,13 +293,22 @@ 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);
> + if (unlikely(dma_heap_exist(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;
> + }
> 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
>
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