linux-kernel - Re: [PATCH 12/15] stackdepot: add refcount for records

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Message-ID: <bb2f8a4f90432452822326b927e8cab58665cd09.camel@mediatek.com>
Date:   Fri, 1 Sep 2023 13:06:36 +0000
From:   Kuan-Ying Lee (李冠穎) 
        <Kuan-Ying.Lee@...iatek.com>
To:     "glider@...gle.com" <glider@...gle.com>,
        "elver@...gle.com" <elver@...gle.com>,
        "andrey.konovalov@...ux.dev" <andrey.konovalov@...ux.dev>
CC:     "andreyknvl@...gle.com" <andreyknvl@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "andreyknvl@...il.com" <andreyknvl@...il.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Kuan-Ying Lee (李冠穎) 
        <Kuan-Ying.Lee@...iatek.com>,
        "eugenis@...gle.com" <eugenis@...gle.com>
Subject: Re: [PATCH 12/15] stackdepot: add refcount for records

On Tue, 2023-08-29 at 19:11 +0200, andrey.konovalov@...ux.dev wrote:
> From: Andrey Konovalov <andreyknvl@...gle.com>
> 
> Add a reference counter for how many times a stack records has been
> added
> to stack depot.
> 
> Do no yet decrement the refcount, this is implemented in one of the
> following patches.
> 
> This is preparatory patch for implementing the eviction of stack
> records
> from the stack depot.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  lib/stackdepot.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 5ad454367379..a84c0debbb9e 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -22,6 +22,7 @@
>  #include <linux/mutex.h>
>  #include <linux/percpu.h>
>  #include <linux/printk.h>
> +#include <linux/refcount.h>
>  #include <linux/slab.h>
>  #include <linux/spinlock.h>
>  #include <linux/stacktrace.h>
> @@ -60,6 +61,7 @@ struct stack_record {
>  	u32 hash;			/* Hash in hash table */
>  	u32 size;			/* Number of stored frames */
>  	union handle_parts handle;
> +	refcount_t count;
>  	unsigned long entries[DEPOT_STACK_MAX_FRAMES];	/* Frames */
>  };
>  
> @@ -348,6 +350,7 @@ depot_alloc_stack(unsigned long *entries, int
> size, u32 hash, void **prealloc)
>  	stack->hash = hash;
>  	stack->size = size;
>  	/* stack->handle is already filled in by depot_init_pool. */
> +	refcount_set(&stack->count, 1);
>  	memcpy(stack->entries, entries, flex_array_size(stack, entries,
> size));
>  
>  	/*
> @@ -452,6 +455,7 @@ depot_stack_handle_t __stack_depot_save(unsigned
> long *entries,
>  	/* Fast path: look the stack trace up without full locking. */
>  	found = find_stack(*bucket, entries, nr_entries, hash);
>  	if (found) {
> +		refcount_inc(&found->count);
>  		read_unlock_irqrestore(&pool_rwlock, flags);
>  		goto exit;
>  	}

Hi Andrey,

There are two find_stack() function calls in __stack_depot_save().

Maybe we need to add refcount_inc() for both two find_stack()?

Thanks,
Kuan-Ying Lee