2021-12-02 11:44:46

by Mauro Carvalho Chehab

Subject: [PATCH] media: ipu3: don't use recursion at the Kernel

The Kernel stack is too small. Doing recursions there is a very
bad idea, as, if something gets wrong, it could lead to data
corruption. So, re-implement cio2_check_fwnode_graph() to avoid
recursion.

Compile-tested only.

Signed-off-by: Mauro Carvalho Chehab <[email protected]>
---
drivers/media/pci/intel/ipu3/ipu3-cio2-main.c | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c b/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c
index 356ea966cf8d..8e4f250a8b56 100644
--- a/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c
+++ b/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c
@@ -1691,16 +1691,15 @@ static int cio2_check_fwnode_graph(struct fwnode_handle *fwnode)
{
struct fwnode_handle *endpoint;

- if (IS_ERR_OR_NULL(fwnode))
- return -EINVAL;
-
- endpoint = fwnode_graph_get_next_endpoint(fwnode, NULL);
- if (endpoint) {
- fwnode_handle_put(endpoint);
- return 0;
+ while (!IS_ERR_OR_NULL(fwnode)) {
+ endpoint = fwnode_graph_get_next_endpoint(fwnode, NULL);
+ if (endpoint) {
+ fwnode_handle_put(endpoint);
+ return 0;
+ }
+ fwnode = fwnode->secondary;
}
-
- return cio2_check_fwnode_graph(fwnode->secondary);
+ return -EINVAL;
}

/**************** PCI interface ****************/
--
2.33.1

2021-12-02 12:32:01

by Daniel Scally

Subject: Re: [PATCH] media: ipu3: don't use recursion at the Kernel

Hi Mauro

On 02/12/2021 11:44, Mauro Carvalho Chehab wrote:
> The Kernel stack is too small. Doing recursions there is a very
> bad idea, as, if something gets wrong, it could lead to data
> corruption.


TIL - I'll bear that in mind in the future, thanks.

> So, re-implement cio2_check_fwnode_graph() to avoid
> recursion.
>
> Compile-tested only.
>
> Signed-off-by: Mauro Carvalho Chehab <[email protected]>


FWIW:

Reviewed-by: Daniel Scally <[email protected]>

Tested-by: Daniel Scally <[email protected]>

> ---
> drivers/media/pci/intel/ipu3/ipu3-cio2-main.c | 17 ++++++++---------
> 1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c b/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c
> index 356ea966cf8d..8e4f250a8b56 100644
> --- a/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c
> +++ b/drivers/media/pci/intel/ipu3/ipu3-cio2-main.c
> @@ -1691,16 +1691,15 @@ static int cio2_check_fwnode_graph(struct fwnode_handle *fwnode)
> {
> struct fwnode_handle *endpoint;
>
> - if (IS_ERR_OR_NULL(fwnode))
> - return -EINVAL;
> -
> - endpoint = fwnode_graph_get_next_endpoint(fwnode, NULL);
> - if (endpoint) {
> - fwnode_handle_put(endpoint);
> - return 0;
> + while (!IS_ERR_OR_NULL(fwnode)) {
> + endpoint = fwnode_graph_get_next_endpoint(fwnode, NULL);
> + if (endpoint) {
> + fwnode_handle_put(endpoint);
> + return 0;
> + }
> + fwnode = fwnode->secondary;
> }
> -
> - return cio2_check_fwnode_graph(fwnode->secondary);
> + return -EINVAL;
> }
>
> /**************** PCI interface ****************/

2021-12-02 12:51:18

by Sakari Ailus

Subject: Re: [PATCH] media: ipu3: don't use recursion at the Kernel

Hi Mauro,

On Thu, Dec 02, 2021 at 12:44:26PM +0100, Mauro Carvalho Chehab wrote:
> The Kernel stack is too small. Doing recursions there is a very
> bad idea, as, if something gets wrong, it could lead to data
> corruption. So, re-implement cio2_check_fwnode_graph() to avoid
> recursion.

Any decent compiler should be able to optimise out tail recursion.

But is checking the secondary pointer even needed these days?
fwnode_graph_get_next_endpoint() does that already, it's not something
drivers should be required to do.

--
Kind regards,

Sakari Ailus