linux-kernel - Re: [PATCH -next 2/5] mm/kmemleak: skip update_checksum for OBJECT_NO

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Date:   Tue, 22 Sep 2020 10:03:48 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Chen Jun <chenjun102@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, rui.xiang@...wei.com,
        weiyongjun1@...wei.com
Subject: Re: [PATCH -next 2/5] mm/kmemleak: skip update_checksum for
 OBJECT_NO_SCAN objects

On Mon, Sep 21, 2020 at 02:00:04AM +0000, Chen Jun wrote:
> From: Wei Yongjun <weiyongjun1@...wei.com>
> 
> Objects marked with OBJECT_NO_SCAN are never scanned.
> So there is no need to update checksum for them.
> 
> Signed-off-by: Wei Yongjun <weiyongjun1@...wei.com>
> Signed-off-by: Chen Jun <chenjun102@...wei.com>
> ---
>  mm/kmemleak.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index b3f603fd9fc3..c09c6b59eda6 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1166,6 +1166,10 @@ static bool update_checksum(struct kmemleak_object *object)
>  {
>  	u32 old_csum = object->checksum;
>  
> +	/* always return false for not scan object */
> +	if (object->flags & OBJECT_NO_SCAN)
> +		return false;

The reason for OBJECT_NO_SCAN is to avoid introducing more false
negatives. The point of the checksum is to reduce the false positives -
i.e. an object that is being modified between scans won't be considered
a (transient) leak even if kmemleak couldn't find a reference pointer to
it.

So please drop this patch.

-- 
Catalin