[PATCH v2] opp: use list iterator only inside the loop

[PATCH v2] opp: use list iterator only inside the loop

[Xiaomeng Tong]

To move the list iterator variable into the list_for_each_entry_*()
macro in the future it should be avoided to use the list iterator
variable after the loop body.

To *never* use the list iterator variable after the loop it was
concluded to use a separate dedicated pointer variable [1].

In this case, use a new variable 'iter' as the list iterator, while
use the old variable 'new_dev' as a dedicated pointer to point to the
found entry. And BUG_ON(!new_dev);.

[1]: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/

Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
---

changes since v1:
 - use BUG_ON(!new_dev); instead of return; (Viresh Kumar)

v1: https://lore.kernel.org/lkml/20220331015818.28045-1-xiam0nd.tong@gmail.com/

---
 drivers/opp/debugfs.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c
index 596c185b5dda..81b2bc4b5f43 100644
--- a/drivers/opp/debugfs.c
+++ b/drivers/opp/debugfs.c
@@ -187,14 +187,18 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table)
 static void opp_migrate_dentry(struct opp_device *opp_dev,
 			       struct opp_table *opp_table)
 {
-	struct opp_device *new_dev;
+	struct opp_device *new_dev = NULL, *iter;
 	const struct device *dev;
 	struct dentry *dentry;
 
 	/* Look for next opp-dev */
-	list_for_each_entry(new_dev, &opp_table->dev_list, node)
-		if (new_dev != opp_dev)
+	list_for_each_entry(iter, &opp_table->dev_list, node)
+		if (iter != opp_dev) {
+			new_dev = iter;
 			break;
+		}
+
+	BUG_ON(!new_dev);
 
 	/* new_dev is guaranteed to be valid here */
 	dev = new_dev->dev;
-- 
2.17.1

Re: [PATCH v2] opp: use list iterator only inside the loop

[Viresh Kumar]

This is V3 and not V2. You need to be careful to update them for every
single version of patch you send.

On 31-03-22, 16:30, Xiaomeng Tong wrote:
> To move the list iterator variable into the list_for_each_entry_*()
> macro in the future it should be avoided to use the list iterator
> variable after the loop body.
> 
> To *never* use the list iterator variable after the loop it was
> concluded to use a separate dedicated pointer variable [1].
> 
> In this case, use a new variable 'iter' as the list iterator, while
> use the old variable 'new_dev' as a dedicated pointer to point to the
> found entry. And BUG_ON(!new_dev);.
> 
> [1]: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/
> 
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
> ---
> 
> changes since v1:
>  - use BUG_ON(!new_dev); instead of return; (Viresh Kumar)
> 
> v1: https://lore.kernel.org/lkml/20220331015818.28045-1-xiam0nd.tong@gmail.com/
> 
> ---
>  drivers/opp/debugfs.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

Looks good now. I will apply it in few days.

-- 
viresh

Re: [PATCH v2] opp: use list iterator only inside the loop

[Xiaomeng Tong]

On Thu, 31 Mar 2022 14:14:53 +0530, Viresh Kumar wrote:
> This is V3 and not V2. You need to be careful to update them for every
> single version of patch you send.
> 

Thank you very much for your patient reply. I got it.

--
Xiaomeng Tong

Re: [PATCH v2] opp: use list iterator only inside the loop

[Viresh Kumar]

On 31-03-22, 16:30, Xiaomeng Tong wrote:
> To move the list iterator variable into the list_for_each_entry_*()
> macro in the future it should be avoided to use the list iterator
> variable after the loop body.
> 
> To *never* use the list iterator variable after the loop it was
> concluded to use a separate dedicated pointer variable [1].
> 
> In this case, use a new variable 'iter' as the list iterator, while
> use the old variable 'new_dev' as a dedicated pointer to point to the
> found entry. And BUG_ON(!new_dev);.
> 
> [1]: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/
> 
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
> ---

Applied. Thanks.

-- 
viresh

Re: [PATCH v2] opp: use list iterator only inside the loop

[Viresh Kumar]

On 31-03-22, 10:36, Xiaomeng Tong wrote:
> The list iterator 'new_dev' will point to a bogus position containing
> HEAD if any one of these conditions is possible: the list is empty or
> no element is found, thus can potentially lead to an invalid memory
> access in 'dev = new_dev->dev;'.

There is no such bug as I explained earlier, why you added this again
despite being discussed ?

> As discussed before,

I just told you not to use such language as this will go in logs, but
you still chose to add it :(

> we should avoid to use a list iterator variable
> outside the loop which is considered harmful[1].
> 
> In this case, use a new variable 'iter' as the list iterator, while
> use the old variable 'new_dev' as a dedicated pointer to point to the
> found entry. And BUG_ON(!new_dev);.

Please look at this on how to write the log, which fixes a very
similar problem.

https://lore.kernel.org/all/20220324071815.61405-1-jakobkoschel@gmail.com/

> 
> [1]:  https://lkml.org/lkml/2022/2/17/1032
> 
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
> ---
> 
> changes since v1:
>  - use BUG_ON(!new_dev); instead of return; (Viresh Kumar)
> 
> v1: https://lore.kernel.org/lkml/20220331015818.28045-1-xiam0nd.tong@gmail.com/
> 
> ---
>  drivers/opp/debugfs.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c
> index 596c185b5dda..81b2bc4b5f43 100644
> --- a/drivers/opp/debugfs.c
> +++ b/drivers/opp/debugfs.c
> @@ -187,14 +187,18 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table)
>  static void opp_migrate_dentry(struct opp_device *opp_dev,
>  			       struct opp_table *opp_table)
>  {
> -	struct opp_device *new_dev;
> +	struct opp_device *new_dev = NULL, *iter;
>  	const struct device *dev;
>  	struct dentry *dentry;
>  
>  	/* Look for next opp-dev */
> -	list_for_each_entry(new_dev, &opp_table->dev_list, node)
> -		if (new_dev != opp_dev)
> +	list_for_each_entry(iter, &opp_table->dev_list, node)
> +		if (iter != opp_dev) {
> +			new_dev = iter;
>  			break;
> +		}
> +
> +	BUG_ON(!new_dev);
>  
>  	/* new_dev is guaranteed to be valid here */
>  	dev = new_dev->dev;
> -- 
> 2.17.1

-- 
viresh

[PATCH v2] opp: use list iterator only inside the loop

[Xiaomeng Tong]

The list iterator 'new_dev' will point to a bogus position containing
HEAD if any one of these conditions is possible: the list is empty or
no element is found, thus can potentially lead to an invalid memory
access in 'dev = new_dev->dev;'.

As discussed before, we should avoid to use a list iterator variable
outside the loop which is considered harmful[1].

In this case, use a new variable 'iter' as the list iterator, while
use the old variable 'new_dev' as a dedicated pointer to point to the
found entry. And BUG_ON(!new_dev);.

[1]:  https://lkml.org/lkml/2022/2/17/1032

Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
---

changes since v1:
 - use BUG_ON(!new_dev); instead of return; (Viresh Kumar)

v1: https://lore.kernel.org/lkml/20220331015818.28045-1-xiam0nd.tong@gmail.com/

---
 drivers/opp/debugfs.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c
index 596c185b5dda..81b2bc4b5f43 100644
--- a/drivers/opp/debugfs.c
+++ b/drivers/opp/debugfs.c
@@ -187,14 +187,18 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table)
 static void opp_migrate_dentry(struct opp_device *opp_dev,
 			       struct opp_table *opp_table)
 {
-	struct opp_device *new_dev;
+	struct opp_device *new_dev = NULL, *iter;
 	const struct device *dev;
 	struct dentry *dentry;
 
 	/* Look for next opp-dev */
-	list_for_each_entry(new_dev, &opp_table->dev_list, node)
-		if (new_dev != opp_dev)
+	list_for_each_entry(iter, &opp_table->dev_list, node)
+		if (iter != opp_dev) {
+			new_dev = iter;
 			break;
+		}
+
+	BUG_ON(!new_dev);
 
 	/* new_dev is guaranteed to be valid here */
 	dev = new_dev->dev;
-- 
2.17.1