diff mbox series

[v4,22/24] dept: Don't create dependencies between different depths in any case

Message ID 1646377603-19730-23-git-send-email-byungchul.park@lge.com (mailing list archive)
State New
Headers show
Series DEPT(Dependency Tracker) | expand

Commit Message

Byungchul Park March 4, 2022, 7:06 a.m. UTC
Dept already prevents creating dependencies between different depths of
the class indicated by *_lock_nested() when the lock acquisitions happen
consecutively.

   lock A0 with depth
   lock_nested A1 with depth + 1
   ...
   unlock A1
   unlock A0

Dept does not create A0 -> A1 dependency in this case, either.

However, once another class cut in, the code becomes problematic. When
Dept tries to create real dependencies, it does not only create real
ones but also wrong ones between different depths of the class.

   lock A0 with depth
   lock B
   lock_nested A1 with depth + 1
   ...
   unlock A1
   unlock B
   unlock A0

Even in this case, Dept should not create A0 -> A1 dependency.

So let Dept not create wrong dependencies between different depths of
the class in any case.

Reported-by: 42.hyeyoo@gmail.com
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/dependency/dept.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

Comments

Hyeonggon Yoo March 4, 2022, 11:39 a.m. UTC | #1
On Fri, Mar 04, 2022 at 04:06:41PM +0900, Byungchul Park wrote:
> Dept already prevents creating dependencies between different depths of
> the class indicated by *_lock_nested() when the lock acquisitions happen
> consecutively.
> 
>    lock A0 with depth
>    lock_nested A1 with depth + 1
>    ...
>    unlock A1
>    unlock A0
> 
> Dept does not create A0 -> A1 dependency in this case, either.
> 
> However, once another class cut in, the code becomes problematic. When
> Dept tries to create real dependencies, it does not only create real
> ones but also wrong ones between different depths of the class.
> 
>    lock A0 with depth
>    lock B
>    lock_nested A1 with depth + 1
>    ...
>    unlock A1
>    unlock B
>    unlock A0
> 
> Even in this case, Dept should not create A0 -> A1 dependency.
> 
> So let Dept not create wrong dependencies between different depths of
> the class in any case.
> 
> Reported-by: 42.hyeyoo@gmail.com
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
>  kernel/dependency/dept.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/kernel/dependency/dept.c b/kernel/dependency/dept.c
> index 5d4efc3..cc1b3a3 100644
> --- a/kernel/dependency/dept.c
> +++ b/kernel/dependency/dept.c
> @@ -1458,14 +1458,7 @@ static void add_wait(struct dept_class *c, unsigned long ip,
>  
>  		eh = dt->ecxt_held + i;
>  		if (eh->ecxt->class != c || eh->nest == ne)
> -			break;
> -	}
> -
> -	for (; i >= 0; i--) {
> -		struct dept_ecxt_held *eh;
> -
> -		eh = dt->ecxt_held + i;
> -		add_dep(eh->ecxt, w);
> +			add_dep(eh->ecxt, w);
>  	}
>  
>  	if (!wait_consumed(w) && !rich_stack) {
> -- 
> 1.9.1
> 
> 

Works as expected, Thanks!
I would report if there is anything else interesting.

Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Byungchul Park March 4, 2022, 11:38 p.m. UTC | #2
On Fri, Mar 04, 2022 at 11:39:29AM +0000, Hyeonggon Yoo wrote:
> Works as expected, Thanks!
> I would report if there is anything else interesting.

Thanks a lot! What you have done is helpful.

Thanks,
Byungchul

> Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> 
> -- 
> Thank you, You are awesome!
> Hyeonggon :-)
diff mbox series

Patch

diff --git a/kernel/dependency/dept.c b/kernel/dependency/dept.c
index 5d4efc3..cc1b3a3 100644
--- a/kernel/dependency/dept.c
+++ b/kernel/dependency/dept.c
@@ -1458,14 +1458,7 @@  static void add_wait(struct dept_class *c, unsigned long ip,
 
 		eh = dt->ecxt_held + i;
 		if (eh->ecxt->class != c || eh->nest == ne)
-			break;
-	}
-
-	for (; i >= 0; i--) {
-		struct dept_ecxt_held *eh;
-
-		eh = dt->ecxt_held + i;
-		add_dep(eh->ecxt, w);
+			add_dep(eh->ecxt, w);
 	}
 
 	if (!wait_consumed(w) && !rich_stack) {