From: David Sterba <dsterba@suse.com>
Date: Tue, 10 Nov 2015 17:54:00 +0000 (+0100)
Subject: btrfs: allocate root item at snapshot ioctl time
X-Git-Url: http://git.hungrycats.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=32b1dd26a8cd02969e49ef308567faec25bb069d;p=linux

btrfs: allocate root item at snapshot ioctl time

The actual snapshot creation is delayed until transaction commit. If we
cannot get enough memory for the root item there, we have to fail the
whole transaction commit which is bad. So we'll allocate the memory at
the ioctl call and pass it along with the pending_snapshot struct. The
potential ENOMEM will be returned to the caller of snapshot ioctl.

Signed-off-by: David Sterba <dsterba@suse.com>
(cherry picked from commit b0c0ea6338d5018e02d27c5315084fb1a5d099f6)
(cherry picked from commit b6e581a7ad2a965960f8b9fe76066fc954258dbe)
---

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index bb6437f78ba8..8f3f0f7b5b7f 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -659,6 +659,13 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
 	if (!pending_snapshot)
 		return -ENOMEM;
 
+	pending_snapshot->root_item = kzalloc(sizeof(struct btrfs_root_item),
+			GFP_NOFS);
+	if (!pending_snapshot->root_item) {
+		ret = -ENOMEM;
+		goto free_pending;
+	}
+
 	atomic_inc(&root->will_be_snapshoted);
 	smp_mb__after_atomic();
 	btrfs_wait_for_no_snapshoting_writes(root);
@@ -738,6 +745,8 @@ fail:
 dec_and_free:
 	if (atomic_dec_and_test(&root->will_be_snapshoted))
 		wake_up_atomic_t(&root->will_be_snapshoted);
+free_pending:
+	kfree(pending_snapshot->root_item);
 	kfree(pending_snapshot);
 
 	return ret;
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index ec9e3b704b48..ff10082096e2 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1366,11 +1366,8 @@ static noinline int create_pending_snapshot(struct btrfs_trans_handle *trans,
 		return 0;
 	}
 
-	new_root_item = kmalloc(sizeof(*new_root_item), GFP_NOFS);
-	if (!new_root_item) {
-		pending->error = -ENOMEM;
-		goto root_item_alloc_fail;
-	}
+	ASSERT(pending->root_item);
+	new_root_item = pending->root_item;
 
 	pending->error = btrfs_find_free_objectid(tree_root, &objectid);
 	if (pending->error)
@@ -1603,7 +1600,7 @@ clear_skip_qgroup:
 	btrfs_clear_skip_qgroup(trans);
 no_free_objectid:
 	kfree(new_root_item);
-root_item_alloc_fail:
+	pending->root_item = NULL;
 	btrfs_free_path(path);
 	return ret;
 }
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 6e755658f0ae..93487babed77 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -138,6 +138,7 @@ struct btrfs_pending_snapshot {
 	struct dentry *dentry;
 	struct inode *dir;
 	struct btrfs_root *root;
+	struct btrfs_root_item *root_item;
 	struct btrfs_root *snap;
 	struct btrfs_qgroup_inherit *inherit;
 	/* block reservation for the operation */