linux-kernel - Re: [PATCH] ext4: Fix memory leak in groupinfo cache name

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Message-ID: <4CEA1208.4060005@cs.helsinki.fi>
Date:	Mon, 22 Nov 2010 08:47:36 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	zeng.zhaoming@...escale.com
CC:	linux-ext4@...r.kernel.org, tytso@....edu,
	adilger.kernel@...ger.ca, mpm@...enic.com, rientjes@...gle.com,
	Zeng Zhaoming <zengzm.kernel@...il.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ext4: Fix memory leak in groupinfo cache name

On 11/22/10 12:02 AM, zeng.zhaoming@...escale.com wrote:
> From: Zeng Zhaoming<zengzm.kernel@...il.com>
>
> please check the discuss with allocator guys.
> http://marc.info/?l=linux-kernel&m=129004890020256&w=2
>
> Get a memory leak 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
>
> ext4 allocate memory for cache name by:
>      namep = kstrdup(name, GFP_KERNEL);
> and reclaim it by:
>      name = kmem_cache_name(cache);
>      kfree(name)
>
> This is ok if allocator only reference to the cache name memory, and return
> the name memory pass to kmem_cache_create() by kmem_cache_name();
> But not true in slub, when using slub, memory leak and double free error appears.
>
> In this patch, we track the cache name memory in ext4, rather than allocator.
>
> Signed-off-by: Zeng Zhaoming<zengzm.kernel@...il.com>
> ---

Hmm. Maybe it's better to change SLAB and SLOB to do kstrdup() 
internally so we can drop it from ext4 code. Matt, are you OK with that?

			Pekka
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