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Message-ID: <20080418051414.GA10568@skywalker>
Date: Fri, 18 Apr 2008 10:44:14 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: Roel Kluin <12o3l@...cali.nl>
Cc: alex@...sterfs.com, sct@...hat.com, akpm@...ux-foundation.org,
adilger@...sterfs.com, linux-ext4@...r.kernel.org,
lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mballoc: fix hot spins after err_freebuddy and
err_freemeta
On Thu, Apr 17, 2008 at 08:29:18PM +0200, Roel Kluin wrote:
> Aneesh Kumar K.V wrote:
>
> > The function needs more changes. For ex:
> >
> > 2279 if (meta_group_info[j] == NULL) {
> > 2280 printk(KERN_ERR "EXT4-fs: can't allocate buddy mem\n");
> > 2281 i--;
> > 2282 goto err_freebuddy;
> > 2283 }
> >
> > That decrement i--; could result in bad value if i == 0;.
>
> Thanks Aneesh,
> ---
> Signed-off-by: Roel Kluin <12o3l@...cali.nl>
> ext4_mb_init_backend() has a variable i of type ext4_group_t. which is typedefined
> in include/linux/ext4_fs_i.h:34 to unsigned long. Since unsigned, i >= 0 is always
> true, so fix hot spins after err_freebuddy and err_freemeta.
> Also when meta_group_info cannot be allocated prevent a decrement of i when zero.
>
> Signed-off-by: Roel Kluin <12o3l@...cali.nl>
> ---
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index ef97f19..2c13dca 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2572,8 +2572,13 @@ static int ext4_mb_init_backend(struct super_block *sb)
> meta_group_info[j] = kzalloc(len, GFP_KERNEL);
> if (meta_group_info[j] == NULL) {
> printk(KERN_ERR "EXT4-fs: can't allocate buddy mem\n");
> - i--;
> - goto err_freebuddy;
> + if (i != 0) {
> + i--;
> + goto err_freebuddy;
> + } else {
> + i = num_meta_group_infos - 1;
> + goto err_freemeta;
> + }
> }
> desc = ext4_get_group_desc(sb, i, NULL);
> if (desc == NULL) {
> @@ -2618,14 +2623,14 @@ static int ext4_mb_init_backend(struct super_block *sb)
> return 0;
>
> err_freebuddy:
> - while (i >= 0) {
> + do {
> kfree(ext4_get_group_info(sb, i));
> - i--;
> - }
> - i = num_meta_group_infos;
> + } while (i-- != 0);
> + i = num_meta_group_infos - 1;
> err_freemeta:
> - while (--i >= 0)
> + do {
> kfree(sbi->s_group_info[i]);
> + } while (i-- != 0);
> iput(sbi->s_buddy_cache);
> err_freesgi:
> kfree(sbi->s_group_info);
>
Won't this also have a memory corruption ? Let's say we fail in the first
loop itslef. That's with i = 0, and since we are using kmalloc.
we may find sbi->s_group_info[0] having some random values. So the
kfree can crash. Why not a simple change like below ?
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 28b5ada..c14f566 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2223,7 +2223,7 @@ static noinline void ext4_mb_store_history(struct ext4_allocation_context *ac)
static int ext4_mb_init_backend(struct super_block *sb)
{
- ext4_group_t i;
+ long i; /* should be able to store group number */
int j, len, metalen;
struct ext4_sb_info *sbi = EXT4_SB(sb);
int num_meta_group_infos =
@@ -2257,6 +2257,7 @@ static int ext4_mb_init_backend(struct super_block *sb)
if (meta_group_info == NULL) {
printk(KERN_ERR "EXT4-fs: can't allocate mem for a "
"buddy group\n");
+ i--;
goto err_freemeta;
}
sbi->s_group_info[i] = meta_group_info;
@@ -2328,7 +2329,7 @@ err_freebuddy:
kfree(ext4_get_group_info(sb, i));
i--;
}
- i = num_meta_group_infos;
+ i = num_meta_group_infos - 1;
err_freemeta:
while (--i >= 0)
kfree(sbi->s_group_info[i]);
--
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