linux-kernel - Re: [PATCH 2/2] sched/debug: fix dentry leak in update_sched_domain

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Message-ID: <YxH+PlfhOV6ZrnrA@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Sep 2022 14:59:42 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Major Chen <major.chen@...sung.com>,
        stable <stable@...nel.org>, Kuyo Chang <kuyo.chang@...iatek.com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH 2/2] sched/debug: fix dentry leak in
 update_sched_domain_debugfs

On Fri, Sep 02, 2022 at 02:31:07PM +0200, Greg Kroah-Hartman wrote:
> Kuyo reports that the pattern of using debugfs_remove(debugfs_lookup())
> leaks a dentry and with a hotplug stress test, the machine eventually
> runs out of memory.
> 
> Fix this up by using the newly created debugfs_lookup_and_remove() call
> instead which properly handles the dentry reference counting logic.

> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> ---
>  kernel/sched/debug.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index bb3d63bdf4ae..667876da8382 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -416,7 +416,7 @@ void update_sched_domain_debugfs(void)
>  		char buf[32];
>  
>  		snprintf(buf, sizeof(buf), "cpu%d", cpu);
> -		debugfs_remove(debugfs_lookup(buf, sd_dentry));
> +		debugfs_lookup_and_remove(buf, sd_dentry);
>  		d_cpu = debugfs_create_dir(buf, sd_dentry);
>  
>  		i = 0;
> -- 
> 2.37.3
>