[PATCH] Re: 2.4.0-test11 ext2 fs corruption

[Alexander Viro]

On Thu, 30 Nov 2000, Daniel Phillips wrote:

> Alexander Viro wrote:
> > Bloody hell...
>
> I don't know if this is the bug he's got, in fact I doubt it, but it's a
> bug and it needs fixing. The problem is, ext2_get_group_desc
> effectively returns two results; one of them is being assigned from on
> conditional paths and the other isn't. This bug will cause - on very
> rare occasions - the wrong group descriptor block to be marked dirty,
> and changes might be lost. I think what we'd see as a result is wrong
> block, inode and directory counts.
>
> The fix below is kind of gross. The way I really want to do the fix is
> to remove one parameter from ext2_get_group_desc and thereby get rid of
> the troublesome side effect for good, but that kind of change isn't
> compatible with 'code freeze'.

Yes, it is. Moreover, correct solution is slightly different and changes
ext2_get_group_desc() semantics. Wait until tomorrow, OK?

However, it's not the source of reported problems. We clearly have b0rken
data in bitmaps themselves.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majo...@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

[Daniel Phillips]

Alexander Viro wrote:
> Bloody hell...

I don't know if this is the bug he's got, in fact I doubt it, but it's a
bug and it needs fixing. The problem is, ext2_get_group_desc
effectively returns two results; one of them is being assigned from on
conditional paths and the other isn't. This bug will cause - on very
rare occasions - the wrong group descriptor block to be marked dirty,
and changes might be lost. I think what we'd see as a result is wrong
block, inode and directory counts.

The fix below is kind of gross. The way I really want to do the fix is
to remove one parameter from ext2_get_group_desc and thereby get rid of
the troublesome side effect for good, but that kind of change isn't
compatible with 'code freeze'.

(linux.2.4.0-test11)

--- fs/ext2/ialloc.c.old Thu Nov 30 00:36:02 2000
+++ fs/ext2/ialloc.c Thu Nov 30 00:36:39 2000
@@ -260,7 +260,7 @@
{
struct super_block * sb;
struct buffer_head * bh;
- struct buffer_head * bh2;
+ struct buffer_head * bh2, * tmpbh2;
int i, j, avefreei;
struct inode * inode;
int bitmap_nr;
@@ -293,10 +293,11 @@
/* I am not yet convinced that this next bit is necessary.
i = dir->u.ext2_i.i_block_group;
for (j = 0; j < sb->u.ext2_sb.s_groups_count; j++) {
- tmp = ext2_get_group_desc (sb, i, &bh2);
+ tmp = ext2_get_group_desc (sb, i, &tmpbh2);
if (tmp &&
(le16_to_cpu(tmp->bg_used_dirs_count) << 8) <
le16_to_cpu(tmp->bg_free_inodes_count)) {
+ bh2 = tmpbh2;
gdp = tmp;
break;
}
@@ -306,7 +307,7 @@
*/
if (!gdp) {
for (j = 0; j < sb->u.ext2_sb.s_groups_count; j++) {
- tmp = ext2_get_group_desc (sb, j, &bh2);
+ tmp = ext2_get_group_desc (sb, j, &tmpbh2);
if (tmp &&
le16_to_cpu(tmp->bg_free_inodes_count) &&
le16_to_cpu(tmp->bg_free_inodes_count) >= avefreei) {
@@ -314,6 +315,7 @@
(le16_to_cpu(tmp->bg_free_blocks_count) >
le16_to_cpu(gdp->bg_free_blocks_count))) {
i = j;
+ bh2 = tmpbh2;
gdp = tmp;
}
}
@@ -326,11 +328,11 @@
* Try to place the inode in its parent directory
*/
i = dir->u.ext2_i.i_block_group;
- tmp = ext2_get_group_desc (sb, i, &bh2);
- if (tmp && le16_to_cpu(tmp->bg_free_inodes_count))
+ tmp = ext2_get_group_desc (sb, i, &tmpbh2);
+ if (tmp && le16_to_cpu(tmp->bg_free_inodes_count)) {
+ bh2 = tmpbh2;
gdp = tmp;
- else
- {
+ } else {
/*
* Use a quadratic hash to find a group with a
* free inode
@@ -339,9 +341,10 @@
i += j;
if (i >= sb->u.ext2_sb.s_groups_count)
i -= sb->u.ext2_sb.s_groups_count;
- tmp = ext2_get_group_desc (sb, i, &bh2);
+ tmp = ext2_get_group_desc (sb, i, &tmpbh2);
if (tmp &&
le16_to_cpu(tmp->bg_free_inodes_count)) {
+ bh2 = tmpbh2;
gdp = tmp;
break;
}
@@ -355,9 +358,10 @@
for (j = 2; j < sb->u.ext2_sb.s_groups_count; j++) {
if (++i >= sb->u.ext2_sb.s_groups_count)
i = 0;
- tmp = ext2_get_group_desc (sb, i, &bh2);
+ tmp = ext2_get_group_desc (sb, i, &tmpbh2);
if (tmp &&
le16_to_cpu(tmp->bg_free_inodes_count)) {
+ bh2 = tmpbh2;
gdp = tmp;
break;
}

--
Daniel