linux-kernel - Re: [PATCH v2 1/2] mm/kmemleak: use object_cache instead of kmemleak_initialized to check in set_track

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Message-ID: <ZNtV+MvSSf3TM+fU@arm.com>
Date:   Tue, 15 Aug 2023 11:39:52 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Xiaolei Wang <xiaolei.wang@...driver.com>
Cc:     akpm@...ux-foundation.org, vbabka@...e.cz, glider@...gle.com,
        andreyknvl@...il.com, zhaoyang.huang@...soc.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm/kmemleak: use object_cache instead of
 kmemleak_initialized to check in set_track_prepare()

On Tue, Aug 15, 2023 at 01:13:57PM +0800, Xiaolei Wang wrote:
> kmemleak_initialized is set in kmemleak_late_init(), which
> also means that there is no call trace which object's memory
> leak is before kmemleak_late_init(), so use object_cache instead
> of kmemleak_initialized to check in set_track_prepare() to avoid
> no call trace records when there is a memory leak in the code
> between kmemleak_init() and kmemleak_late_init().
> 
> unreferenced object 0xc674ca80 (size 64):
>  comm "swapper/0", pid 1, jiffies 4294938337 (age 204.880s)
>  hex dump (first 32 bytes):
>   80 55 75 c6 80 54 75 c6 00 55 75 c6 80 52 75 c6 .Uu..Tu..Uu..Ru.
>   00 53 75 c6 00 00 00 00 00 00 00 00 00 00 00 00 .Su..........
> 
> Fixes: 56a61617dd22 ("mm: use stack_depot for recording kmemleak's backtrace")
> Signed-off-by: Xiaolei Wang <xiaolei.wang@...driver.com>
> ---
>  mm/kmemleak.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index a2d34226e3c8..04bb4cdbb402 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -610,7 +610,8 @@ static noinline depot_stack_handle_t set_track_prepare(void)
>  	unsigned long entries[MAX_TRACE];
>  	unsigned int nr_entries;
>  
> -	if (!kmemleak_initialized)
> +	/*Use object_cache to determine whether kmemleak_init() is complete*/

Nitpick: please add spaces after/before the comment delimiters. I'd also
make it clearer that it's not about kmemleak being initialised but
rather the stack depot. E.g.:

	/*
	 * Use object_cache to determine whether kmemleak_init() has
	 * been invoked. stack_depot_early_init() is called before
	 * kmemleak_init() in mm_core_init().
	 */

> +	if (!object_cache)
>  		return 0;
>  	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
>  	trace_handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);

Otherwise:

Reviewed-by: Catalin Marinas <catalin.marinas@....com>