Theodore Tso wrote:
> On Thu, May 15, 2008 at 12:17:11AM +0530, Aneesh Kumar K.V wrote:
>> @@ -3134,8 +3135,7 @@ static void ext4_mb_use_inode_pa(struct ext4_allocation_context *ac,
>> static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac,
>> struct ext4_prealloc_space *pa)
>> {
>> - unsigned len = ac->ac_o_ex.fe_len;
>> -
>> + unsigned int len = ac->ac_o_ex.fe_len;
>> ext4_get_group_no_and_offset(ac->ac_sb, pa->pa_pstart,
>> &ac->ac_b_ex.fe_group,
>> &ac->ac_b_ex.fe_start);
>> --
>
> This change had nothing to do with fixing the use of unitialized data,
> but when I started looking more closely, it raised a potential signed
> vs. unsigned issue: ac_o_ex is a struct ext4_free_extent, and fe_len
> is an int.
>
> So here we are assigning an int to an unsigned int. Later, len is
> assigned to ac_b_ex.len, which means assigning an unsigned int to an
> int. In other places, fe_len (an int) is compared against pa_free
> (which is an unsigned short), and fe_len gets assined to pa_free, once
> again mixing signed and unsigned.
>
> Can someone who is really familiar with this code check this out? I
> think the following pseudo-patch to mballoc.h might be in order:
>
> struct ext4_free_extent {
> ext4_lblk_t fe_logical;
> ext4_grpblk_t fe_start;
> ext4_group_t fe_group;
> - int fe_len;
> + unsigned int fe_len;
> };
Hm, ok, so what's going on here:
ext4_mb_normalize_group_request()
{
...
if (EXT4_SB(sb)->s_stripe)
ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_stripe;
else
ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;
...
}
and that's a long:
unsigned long s_mb_group_prealloc;
Oh, but that's only ever assigned as
sbi->s_mb_group_prealloc = MB_DEFAULT_GROUP_PREALLOC;
which is
/*
* default group prealloc size 512 blocks
*/
#define MB_DEFAULT_GROUP_PREALLOC 512
so it's fine... but why are we carrying around a field in the sbi to
hold a constant that cannot be changed runtime?
-Eric
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