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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,
        linux-ext4@...r.kernel.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        will@...nel.org, tglx@...utronix.de, rostedt@...dmis.org,
        joel@...lfernandes.org, sashal@...nel.org, daniel.vetter@...ll.ch,
        chris@...is-wilson.co.uk, duyuyang@...il.com,
        johannes.berg@...el.com, tj@...nel.org, tytso@....edu,
        willy@...radead.org, david@...morbit.com, amir73il@...il.com,
        bfields@...ldses.org, gregkh@...uxfoundation.org,
        kernel-team@....com, linux-mm@...ck.org, akpm@...ux-foundation.org,
        mhocko@...nel.org, minchan@...nel.org, hannes@...xchg.org,
        vdavydov.dev@...il.com, sj@...nel.org, jglisse@...hat.com,
        dennis@...nel.org, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, vbabka@...e.cz, ngupta@...are.org,
        linux-block@...r.kernel.org, paolo.valente@...aro.org,
        josef@...icpanda.com, linux-fsdevel@...r.kernel.org,
        viro@...iv.linux.org.uk, jack@...e.cz, jack@...e.com,
        jlayton@...nel.org, dan.j.williams@...el.com, hch@...radead.org,
        djwong@...nel.org, dri-devel@...ts.freedesktop.org,
        airlied@...ux.ie, rodrigosiqueiramelo@...il.com,
        melissa.srw@...il.com, hamohammed.sa@...il.com
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 :-)

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