btrfs: allocate raid type kobjects dynamically

We are currently allocating space_info objects in an array when we allocate space_info. When a user does something like:

# btrfs balance start -mconvert=raid1 -dconvert=raid1 /mnt
# btrfs balance start -mconvert=single -dconvert=single /mnt -f
# btrfs balance start -mconvert=raid1 -dconvert=raid1 /

We can end up with memory corruption since the kobject hasn't been reinitialized properly and the name pointer was left set.

The rationale behind allocating them statically was to avoid creating a separate kobject container that just contained the raid type. It used the index in the array to determine the index.

Ultimately, though, this wastes more memory than it saves in all but the most complex scenarios and introduces kobject lifetime questions.

This patch allocates the kobjects dynamically instead. Note that we also remove the kobject_get/put of the parent kobject since kobject_add and kobject_del do that internally.

---
 fs/btrfs/ctree.h       |    8 +++++++-
 fs/btrfs/extent-tree.c |   39 ++++++++++++++++++++++++++-------------
 fs/btrfs/sysfs.c       |    5 +++--
 3 files changed, 36 insertions(+), 16 deletions(-)

@@ -1113,6 +1113,12 @@ struct btrfs_qgroup_limit_item {
 	__le64 rsv_excl;
 } __attribute__ ((__packed__));
 
+/* For raid type sysfs entries */
+struct raid_kobject {
+	int raid_type;
+	struct kobject kobj;
+};
+
 struct btrfs_space_info {
 	spinlock_t lock;
 

@@ -1163,7 +1169,7 @@ struct btrfs_space_info {
 	wait_queue_head_t wait;
 
 	struct kobject kobj;
-	struct kobject block_group_kobjs[BTRFS_NR_RAID_TYPES];
+	struct kobject *block_group_kobjs[BTRFS_NR_RAID_TYPES];
 };
 
 #define	BTRFS_BLOCK_RSV_GLOBAL		1

@@ -3401,10 +3401,8 @@ static int update_space_info(struct btrf
 		return ret;
 	}
 
-	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
+	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
 		INIT_LIST_HEAD(&found->block_groups[i]);
-		kobject_init(&found->block_group_kobjs[i], &btrfs_raid_ktype);
-	}
 	init_rwsem(&found->groups_sem);
 	spin_lock_init(&found->lock);
 	found->flags = flags & BTRFS_BLOCK_GROUP_TYPE_MASK;

@@ -8327,8 +8325,9 @@ int btrfs_free_block_groups(struct btrfs
 		list_del(&space_info->list);
 		for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
 			struct kobject *kobj;
-			kobj = &space_info->block_group_kobjs[i];
-			if (kobj->parent) {
+			kobj = space_info->block_group_kobjs[i];
+			space_info->block_group_kobjs[i] = NULL;
+			if (kobj) {
 				kobject_del(kobj);
 				kobject_put(kobj);
 			}

@@ -8352,17 +8351,26 @@ static void __link_block_group(struct bt
 	up_write(&space_info->groups_sem);
 
 	if (first) {
-		struct kobject *kobj = &space_info->block_group_kobjs[index];
+		struct raid_kobject *rkobj;
 		int ret;
 
-		kobject_get(&space_info->kobj); /* put in release */
-		ret = kobject_add(kobj, &space_info->kobj, "%s",
-				  get_raid_name(index));
+		rkobj = kzalloc(sizeof(*rkobj), GFP_KERNEL);
+		if (!rkobj)
+			goto out_err;
+		rkobj->raid_type = index;
+		kobject_init(&rkobj->kobj, &btrfs_raid_ktype);
+		ret = kobject_add(&rkobj->kobj, &space_info->kobj,
+				  "%s", get_raid_name(index));
 		if (ret) {
-			pr_warn("BTRFS: failed to add kobject for block cache. ignoring.\n");
-			kobject_put(&space_info->kobj);
+			kobject_put(&rkobj->kobj);
+			goto out_err;
 		}
+		space_info->block_group_kobjs[index] = &rkobj->kobj;
 	}
+
+	return;
+out_err:
+	pr_warn("BTRFS: failed to add kobject for block cache. ignoring.\n");
 }
 
 static struct btrfs_block_group_cache *

@@ -8697,6 +8705,7 @@ int btrfs_remove_block_group(struct btrf
 	struct btrfs_root *tree_root = root->fs_info->tree_root;
 	struct btrfs_key key;
 	struct inode *inode;
+	struct kobject *kobj = NULL;
 	int ret;
 	int index;
 	int factor;

@@ -8796,11 +8805,15 @@ int btrfs_remove_block_group(struct btrf
 	 */
 	list_del_init(&block_group->list);
 	if (list_empty(&block_group->space_info->block_groups[index])) {
-		kobject_del(&block_group->space_info->block_group_kobjs[index]);
-		kobject_put(&block_group->space_info->block_group_kobjs[index]);
+		kobj = block_group->space_info->block_group_kobjs[index];
+		block_group->space_info->block_group_kobjs[index] = NULL;
 		clear_avail_alloc_bits(root->fs_info, block_group->flags);
 	}
 	up_write(&block_group->space_info->groups_sem);
+	if (kobj) {
+		kobject_del(kobj);
+		kobject_put(kobj);
+	}
 
 	if (block_group->cached == BTRFS_CACHE_STARTED)
 		wait_block_group_cache_done(block_group);

@@ -254,6 +254,7 @@ static ssize_t global_rsv_reserved_show(
 BTRFS_ATTR(global_rsv_reserved, 0444, global_rsv_reserved_show);
 
 #define to_space_info(_kobj) container_of(_kobj, struct btrfs_space_info, kobj)
+#define to_raid_kobj(_kobj) container_of(_kobj, struct raid_kobject, kobj)
 
 static ssize_t raid_bytes_show(struct kobject *kobj,
 			       struct kobj_attribute *attr, char *buf);

@@ -266,7 +267,7 @@ static ssize_t raid_bytes_show(struct ko
 {
 	struct btrfs_space_info *sinfo = to_space_info(kobj->parent);
 	struct btrfs_block_group_cache *block_group;
-	int index = kobj - sinfo->block_group_kobjs;
+	int index = to_raid_kobj(kobj)->raid_type;
 	u64 val = 0;
 
 	down_read(&sinfo->groups_sem);

@@ -288,7 +289,7 @@ static struct attribute *raid_attributes
 
 static void release_raid_kobj(struct kobject *kobj)
 {
-	kobject_put(kobj->parent);
+	kfree(to_raid_kobj(kobj));
 }
 
 struct kobj_type btrfs_raid_ktype = {

Jeff Mahoney
SUSE Labs

A different lockdep chain, from test btrfs/014:

[  229.850151] ======================================================
[  229.850788] [ INFO: possible circular locking dependency detected ]
[  229.850788] 3.15.0-rc7-default+ #146 Tainted: G        W
[  229.850788] -------------------------------------------------------
[  229.850788] btrfs/26558 is trying to acquire lock:
[  229.850788]  (s_active#149){++++.+}, at: [<ffffffff811ee787>] kernfs_remove+0x27/0x40
[  229.850788]
[  229.850788] but task is already holding lock:
[  229.850788]  (&found->groups_sem){++++..}, at: [<ffffffffa0023abe>] btrfs_remove_block_group+0x24e/0x580 [btrfs]
[  229.850788]
[  229.850788] which lock already depends on the new lock.
[  229.850788]
[  229.850788]
[  229.850788] the existing dependency chain (in reverse order) is:
[  229.850788]
-> #1 (&found->groups_sem){++++..}:
[  229.850788]        [<ffffffff810b0662>] lock_acquire+0x92/0x120
[  229.850788]        [<ffffffff81a0bedc>] down_read+0x4c/0xa0
[  229.850788]        [<ffffffffa004babe>] raid_bytes_show+0x3e/0xd0 [btrfs]
[  229.850788]        [<ffffffff813b9ef6>] kobj_attr_show+0x16/0x20
[  229.850788]        [<ffffffff811f04e9>] sysfs_kf_seq_show+0xd9/0x230
[  229.850788]        [<ffffffff811eec56>] kernfs_seq_show+0x26/0x30
[  229.850788]        [<ffffffff8119ec8f>] seq_read+0xef/0x410
[  229.850788]        [<ffffffff811efa35>] kernfs_fop_read+0x125/0x180
[  229.850788]        [<ffffffff81179fe4>] vfs_read+0xb4/0x180
[  229.850788]        [<ffffffff8117a269>] SyS_read+0x59/0xd0
[  229.850788]        [<ffffffff81a16cd2>] system_call_fastpath+0x16/0x1b
[  229.850788]
-> #0 (s_active#149){++++.+}:
[  229.850788]        [<ffffffff810afc5c>] __lock_acquire+0x1c4c/0x1fa0
[  229.850788]        [<ffffffff810b0662>] lock_acquire+0x92/0x120
[  229.850788]        [<ffffffff811edc07>] __kernfs_remove+0x2b7/0x380
[  229.850788]        [<ffffffff811ee787>] kernfs_remove+0x27/0x40
[  229.850788]        [<ffffffff811f0b3a>] sysfs_remove_dir+0x5a/0x90
[  229.850788]        [<ffffffff813ba028>] kobject_del+0x18/0x90
[  229.850788]        [<ffffffffa0023cb2>] btrfs_remove_block_group+0x442/0x580 [btrfs]
[  229.850788]        [<ffffffffa005caf4>] btrfs_relocate_chunk+0x624/0x770 [btrfs]
[  229.850788]        [<ffffffffa005f652>] btrfs_balance+0x902/0xf50 [btrfs]
[  229.850788]        [<ffffffffa006b090>] btrfs_ioctl_balance+0x1e0/0x350 [btrfs]
[  229.850788]        [<ffffffffa006d4a9>] btrfs_ioctl+0xc39/0x1830 [btrfs]
[  229.850788]        [<ffffffff8118c381>] do_vfs_ioctl+0x91/0x560
[  229.850788]        [<ffffffff8118c8a3>] SyS_ioctl+0x53/0x80
[  229.850788]        [<ffffffff81a16cd2>] system_call_fastpath+0x16/0x1b
[  229.850788]
[  229.850788] other info that might help us debug this:
[  229.850788]
[  229.850788]  Possible unsafe locking scenario:
[  229.850788]
[  229.850788]        CPU0                    CPU1
[  229.850788]        ----                    ----
[  229.850788]   lock(&found->groups_sem);
[  229.850788]                                lock(s_active#149);
[  229.850788]                                lock(&found->groups_sem);
[  229.850788]   lock(s_active#149);
[  229.850788]
[  229.850788]  *** DEADLOCK ***
[  229.850788]
[  229.850788] 5 locks held by btrfs/26558:
[  229.850788]  #0:  (sb_writers#11){.+.+.+}, at: [<ffffffff8119a828>] mnt_want_write_file+0x28/0x60
[  229.850788]  #1:  (&fs_info->volume_mutex){+.+.+.}, at: [<ffffffffa006afe1>] btrfs_ioctl_balance+0x131/0x350 [btrfs]
[  229.850788]  #2:  (sb_internal){.+.+..}, at: [<ffffffffa0035436>] start_transaction+0x456/0x550 [btrfs]
[  229.850788]  #3:  (&fs_info->chunk_mutex){+.+...}, at: [<ffffffffa005927e>] lock_chunks+0x1e/0x20 [btrfs]
[  229.850788]  #4:  (&found->groups_sem){++++..}, at: [<ffffffffa0023abe>] btrfs_remove_block_group+0x24e/0x580 [btrfs]
[  229.850788]
[  229.850788] stack backtrace:
[  229.850788] CPU: 1 PID: 26558 Comm: btrfs Tainted: G        W     3.15.0-rc7-default+ #146
[  229.850788] Hardware name: Intel Corporation Santa Rosa platform/Matanzas, BIOS TSRSCRB1.86C.0047.B00.0610170821 10/17/06
[  229.850788]  ffffffff8281faf0 ffff8800652a1818 ffffffff81a07898 0000000000000001
[  229.850788]  ffffffff82827310 ffff8800652a1868 ffffffff810acb74 00000000001d4500
[  229.850788]  ffff8800652a18e8 0000000000000004 ffff880075e0ac78 0000000000000004
[  229.850788] Call Trace:
[  229.850788]  [<ffffffff81a07898>] dump_stack+0x51/0x71
[  229.850788]  [<ffffffff810acb74>] print_circular_bug+0x214/0x310
[  229.850788]  [<ffffffff810afc5c>] __lock_acquire+0x1c4c/0x1fa0
[  229.850788]  [<ffffffff811ee787>] ? kernfs_remove+0x27/0x40
[  229.850788]  [<ffffffff810b0662>] lock_acquire+0x92/0x120
[  229.850788]  [<ffffffff811ee787>] ? kernfs_remove+0x27/0x40
[  229.850788]  [<ffffffff81a0bb39>] ? mutex_unlock+0x9/0x10
[  229.850788]  [<ffffffff811edc07>] __kernfs_remove+0x2b7/0x380
[  229.850788]  [<ffffffff811ee787>] ? kernfs_remove+0x27/0x40
[  229.850788]  [<ffffffff811ee77f>] ? kernfs_remove+0x1f/0x40
[  229.850788]  [<ffffffff811ee787>] kernfs_remove+0x27/0x40
[  229.850788]  [<ffffffff811f0b3a>] sysfs_remove_dir+0x5a/0x90
[  229.850788]  [<ffffffff813ba028>] kobject_del+0x18/0x90
[  229.850788]  [<ffffffffa0023cb2>] btrfs_remove_block_group+0x442/0x580 [btrfs]
[  229.850788]  [<ffffffff810b112d>] ? trace_hardirqs_on_caller+0x11d/0x1e0
[  229.850788]  [<ffffffffa005caf4>] btrfs_relocate_chunk+0x624/0x770 [btrfs]
[  229.850788]  [<ffffffffa0056ac6>] ? release_extent_buffer+0x36/0xe0 [btrfs]
[  229.850788]  [<ffffffffa005706a>] ? free_extent_buffer+0x4a/0xc0 [btrfs]
[  229.850788]  [<ffffffffa0057080>] ? free_extent_buffer+0x60/0xc0 [btrfs]
[  229.850788]  [<ffffffffa005f652>] btrfs_balance+0x902/0xf50 [btrfs]
[  229.850788]  [<ffffffffa006b090>] ? btrfs_ioctl_balance+0x1e0/0x350 [btrfs]
[  229.850788]  [<ffffffff8116e3fa>] ? kmem_cache_alloc_trace+0x12a/0x180
[  229.850788]  [<ffffffffa006b090>] btrfs_ioctl_balance+0x1e0/0x350 [btrfs]
[  229.850788]  [<ffffffffa006c870>] ? update_ioctl_balance_args+0x130/0x130 [btrfs]
[  229.850788]  [<ffffffffa006d4a9>] btrfs_ioctl+0xc39/0x1830 [btrfs]
[  229.850788]  [<ffffffff8118c381>] do_vfs_ioctl+0x91/0x560
[  229.850788]  [<ffffffff81197959>] ? __fget_light+0x9/0x70
[  229.850788]  [<ffffffff811979c9>] ? __fdget+0x9/0x20
[  229.850788]  [<ffffffff8118c8a3>] SyS_ioctl+0x53/0x80
[  229.850788]  [<ffffffff81a16cd2>] system_call_fastpath+0x16/0x1b

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Are you sure this one was with the new patch? We shouldn't be holding groups_sem anymore in btrfs_remove_block_group while performing the kobject ops.

- -Jeff

- --
Jeff Mahoney
SUSE Labs
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Right, the lockdep call chain does not match the sources. I've rebuilt & rebooted with v3 and am not seeing any of the sysfs related messages.

The fix is for stable 3.13+ and even better if it lands in 3.15, as it fixes a double-free that can randomly hit other subsystems due to frequent kmalloc-32 slab reuse,
(eg. https://bugzilla.kernel.org/show_bug.cgi?id=72461).

Thanks Jeff, one small thing below:

                                               ^^^^^^^^^^^^

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Sigh. Yep.

- -Jeff

- --
Jeff Mahoney
SUSE Labs
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