mballoc: fix hot spins after err_freebuddy and err_freemeta

fs/ext4/mballoc.c +1 -4

 err_freebuddy:
-	while (i >= 0) {
+	do {
 		kfree(ext4_get_group_info(sb, i));
-		i--;
-	}
-	i = num_meta_group_infos;

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;.

Quoted 9 lines · Aneesh Kumar K.V

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 <[email protected]>

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 <[email protected]>

---

fs/ext4/mballoc.c +8 -6

index ef97f19..2c13dca 100644
@@ -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;

Quoted 60 lines · Roel Kluin

Quoted 9 lines · Aneesh Kumar K.V

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 <[email protected]>

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 <[email protected]>

---

fs/ext4/mballoc.c +12 -7

index ef97f19..2c13dca 100644
@@ -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);

fs/ext4/mballoc.c static int ext4_mb_init_backend(struct super_block *sb) · line 2636

Quoted 3 lines

fs/ext4/mballoc.c +0 -0

 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 ?

Quoted 12 lines · Aneesh Kumar K.V

Quoted 11 lines · Roel Kluin

Quoted 9 lines · Aneesh Kumar K.V

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;.

Quoted 5 lines

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.