linux-kernel - Re: [PATCH v4 22/24] dept: Don't create dependencies between different depths in any case

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Date:   Fri, 4 Mar 2022 11:39:29 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Byungchul Park <byungchul.park@....com>
Cc:     torvalds@...ux-foundation.org, damien.lemoal@...nsource.wdc.com,
        linux-ide@...r.kernel.org, adilger.kernel@...ger.ca,
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Subject: Re: [PATCH v4 22/24] dept: Don't create dependencies between
 different depths in any case

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@...il.com
> Signed-off-by: Byungchul Park <byungchul.park@....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@...il.com>

-- 
Thank you, You are awesome!
Hyeonggon :-)