linux-kernel - Re: [PATCH] slub: operate cache name memory same to slab and slob

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Date:	Thu, 18 Nov 2010 15:15:08 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	b32542@...escale.com
Cc:	linux-mm@...ck.org, cl@...ux-foundation.org,
	penberg@...helsinki.fi, tytso@....edu,
	linux-kernel@...r.kernel.org,
	Zeng Zhaoming <zengzm.kernel@...il.com>
Subject: Re: [PATCH] slub: operate cache name memory same to slab and slob

On Thu, 2010-11-18 at 11:00 +0800, b32542@...escale.com wrote:
> From: Zeng Zhaoming <zengzm.kernel@...il.com>
> 
> Get a memory leak complaint about ext4:
>   comm "mount", pid 1159, jiffies 4294904647 (age 6077.804s)
>   hex dump (first 32 bytes):
>     65 78 74 34 5f 67 72 6f 75 70 69 6e 66 6f 5f 31  ext4_groupinfo_1
>     30 00 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5  0.kkkkkkkkkkkkk.
>   backtrace:
>     [<c068ade3>] kmemleak_alloc+0x93/0xd0
>     [<c024e54c>] __kmalloc_track_caller+0x30c/0x380
>     [<c02269d3>] kstrdup+0x33/0x60
>     [<c0318a70>] ext4_mb_init+0x4e0/0x550
>     [<c0304e0e>] ext4_fill_super+0x1e6e/0x2f60
>     [<c0261140>] mount_bdev+0x1c0/0x1f0
>     [<c02fc00f>] ext4_mount+0x1f/0x30
>     [<c02603d8>] vfs_kern_mount+0x78/0x250
>     [<c026060e>] do_kern_mount+0x3e/0x100
>     [<c027b4c2>] do_mount+0x2e2/0x780
>     [<c027ba04>] sys_mount+0xa4/0xd0
>     [<c010429f>] sysenter_do_call+0x12/0x38
>     [<ffffffff>] 0xffffffff
> 
> It is cause by slub manage the cache name different from slab and slob.
> In slab and slob, only reference to name, alloc and reclaim the memory
> is the duty of the code that invoked kmem_cache_create().
> 
> In slub, cache name duplicated when create. This ambiguity will cause
> some memory leaks and double free if kmem_cache_create() pass a
> dynamic malloc cache name.

I don't get it.

Caller allocates X, passes X to slub, slub duplicates X as X', and
properly frees X', then caller frees X. Yes, that's silly, but where's
the leak?

But slub and slab should obviously both manage names in the same way,
namely the historical "caller allocates" way. So:

Acked-by: Matt Mackall <mpm@...enic.com>

> ---
>  mm/slub.c |   11 +----------
>  1 files changed, 1 insertions(+), 10 deletions(-)
>  mode change 100644 => 100755 mm/slub.c
> 
> diff --git a/mm/slub.c b/mm/slub.c
> old mode 100644
> new mode 100755
> index 981fb73..a223e08
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -209,7 +209,6 @@ static inline int sysfs_slab_alias(struct kmem_cache *s, const char *p)
>  							{ return 0; }
>  static inline void sysfs_slab_remove(struct kmem_cache *s)
>  {
> -	kfree(s->name);
>  	kfree(s);
>  }
>  
> @@ -3228,7 +3227,6 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
>  		size_t align, unsigned long flags, void (*ctor)(void *))
>  {
>  	struct kmem_cache *s;
> -	char *n;
>  
>  	if (WARN_ON(!name))
>  		return NULL;
> @@ -3252,25 +3250,19 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
>  		return s;
>  	}
>  
> -	n = kstrdup(name, GFP_KERNEL);
> -	if (!n)
> -		goto err;
> -
>  	s = kmalloc(kmem_size, GFP_KERNEL);
>  	if (s) {
> -		if (kmem_cache_open(s, n,
> +		if (kmem_cache_open(s, name,
>  				size, align, flags, ctor)) {
>  			list_add(&s->list, &slab_caches);
>  			if (sysfs_slab_add(s)) {
>  				list_del(&s->list);
> -				kfree(n);
>  				kfree(s);
>  				goto err;
>  			}
>  			up_write(&slub_lock);
>  			return s;
>  		}
> -		kfree(n);
>  		kfree(s);
>  	}
>  err:
> @@ -4421,7 +4413,6 @@ static void kmem_cache_release(struct kobject *kobj)
>  {
>  	struct kmem_cache *s = to_slab(kobj);
>  
> -	kfree(s->name);
>  	kfree(s);
>  }
>  


-- 
Mathematics is the supreme nostalgia of our time.


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