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SubjectRe: [PATCH v2] mballoc: fix hot spins after err_freebuddy and err_freemeta
On Fri, Apr 18, 2008 at 10:44:14AM +0530, Aneesh Kumar K.V wrote:
> 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@tiscali.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@tiscali.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 ?
>

Updated one.

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 28b5ada..572d809 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;
@@ -2328,10 +2329,12 @@ 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)
+ while (i >= 0) {
kfree(sbi->s_group_info[i]);
+ i--;
+ }
iput(sbi->s_buddy_cache);
err_freesgi:
kfree(sbi->s_group_info);

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