linux-kernel - Re: [PATCH] mm/z3fold: silence kmemleak false positives of slots

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Date:   Tue, 26 May 2020 10:11:07 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Qian Cai <cai@....pw>
Cc:     akpm@...ux-foundation.org, vitaly.wool@...sulko.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/z3fold: silence kmemleak false positives of slots

On Fri, May 22, 2020 at 06:00:52PM -0400, Qian Cai wrote:
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 8c3bb5e508b8..460b0feced26 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -43,6 +43,7 @@
>  #include <linux/spinlock.h>
>  #include <linux/zpool.h>
>  #include <linux/magic.h>
> +#include <linux/kmemleak.h>
>  
>  /*
>   * NCHUNKS_ORDER determines the internal allocation granularity, effectively
> @@ -215,6 +216,8 @@ static inline struct z3fold_buddy_slots *alloc_slots(struct z3fold_pool *pool,
>  				 (gfp & ~(__GFP_HIGHMEM | __GFP_MOVABLE)));
>  
>  	if (slots) {
> +		/* It will be freed separately in free_handle(). */
> +		kmemleak_not_leak(slots);
>  		memset(slots->slot, 0, sizeof(slots->slot));
>  		slots->pool = (unsigned long)pool;
>  		rwlock_init(&slots->lock);

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

An alternative would have been a kmemleak_alloc(zhdr, sizeof(*zhdr), 1)
in init_z3fold_page() and a corresponding kmemleak_free() in
free_z3fold_page() (if !headless) since kmemleak doesn't track page
allocations. The advantage is that it would track the slots in case
there is a leak. But if the code is clear enough that the slots are
freed, just keep the kmemleak_not_leak() annotation.

-- 
Catalin