[PATCH] btrfs: qgroup: fix sleep from invalid context bug in update_qgroup_limit_item()

[ChenXiaoSong]

Syzkaller reported BUG as follows:

  BUG: sleeping function called from invalid context at
       include/linux/sched/mm.h:274
  Call Trace:
   <TASK>
   dump_stack_lvl+0xcd/0x134
   __might_resched.cold+0x222/0x26b
   kmem_cache_alloc+0x2e7/0x3c0
   update_qgroup_limit_item+0xe1/0x390
   btrfs_qgroup_inherit+0x147b/0x1ee0
   create_subvol+0x4eb/0x1710
   btrfs_mksubvol+0xfe5/0x13f0
   __btrfs_ioctl_snap_create+0x2b0/0x430
   btrfs_ioctl_snap_create_v2+0x25a/0x520
   btrfs_ioctl+0x2a1c/0x5ce0
   __x64_sys_ioctl+0x193/0x200
   do_syscall_64+0x35/0x80

Fix this by introducing __update_qgroup_limit_item() helper, allocate
memory outside of the spin lock.

Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
---
 fs/btrfs/qgroup.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 9334c3157c22..99a61cc04b68 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -768,11 +768,11 @@ static int del_qgroup_item(struct btrfs_trans_handle *trans, u64 qgroupid)
 	return ret;
 }
 
-static int update_qgroup_limit_item(struct btrfs_trans_handle *trans,
-				    struct btrfs_qgroup *qgroup)
+static int __update_qgroup_limit_item(struct btrfs_trans_handle *trans,
+				      struct btrfs_qgroup *qgroup,
+				      struct btrfs_path *path)
 {
 	struct btrfs_root *quota_root = trans->fs_info->quota_root;
-	struct btrfs_path *path;
 	struct btrfs_key key;
 	struct extent_buffer *l;
 	struct btrfs_qgroup_limit_item *qgroup_limit;
@@ -783,10 +783,6 @@ static int update_qgroup_limit_item(struct btrfs_trans_handle *trans,
 	key.type = BTRFS_QGROUP_LIMIT_KEY;
 	key.offset = qgroup->qgroupid;
 
-	path = btrfs_alloc_path();
-	if (!path)
-		return -ENOMEM;
-
 	ret = btrfs_search_slot(trans, quota_root, &key, path, 0, 1);
 	if (ret > 0)
 		ret = -ENOENT;
@@ -806,6 +802,21 @@ static int update_qgroup_limit_item(struct btrfs_trans_handle *trans,
 	btrfs_mark_buffer_dirty(l);
 
 out:
+	return ret;
+}
+
+static int update_qgroup_limit_item(struct btrfs_trans_handle *trans,
+				    struct btrfs_qgroup *qgroup)
+{
+	struct btrfs_path *path;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	ret = __update_qgroup_limit_item(trans, qgroup, path);
+
 	btrfs_free_path(path);
 	return ret;
 }
@@ -2860,6 +2871,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 	bool need_rescan = false;
 	u32 level_size = 0;
 	u64 nums;
+	struct btrfs_path *path;
 
 	/*
 	 * There are only two callers of this function.
@@ -2935,6 +2947,11 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 		ret = 0;
 	}
 
+	path = btrfs_alloc_path();
+	if (!path) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
 	spin_lock(&fs_info->qgroup_lock);
 
@@ -2950,8 +2967,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 		dstgroup->max_excl = inherit->lim.max_excl;
 		dstgroup->rsv_rfer = inherit->lim.rsv_rfer;
 		dstgroup->rsv_excl = inherit->lim.rsv_excl;
-
-		ret = update_qgroup_limit_item(trans, dstgroup);
+		ret = __update_qgroup_limit_item(trans, dstgroup, path);
 		if (ret) {
 			qgroup_mark_inconsistent(fs_info);
 			btrfs_info(fs_info,
@@ -3053,6 +3069,7 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid,
 
 unlock:
 	spin_unlock(&fs_info->qgroup_lock);
+	btrfs_free_path(path);
 	if (!ret)
 		ret = btrfs_sysfs_add_one_qgroup(fs_info, dstgroup);
 out:
-- 
2.31.1