Btrfs: qgroup: Introduce a may_use to account space_info->bytes_may_use.

Currently, for pre_alloc or delay_alloc, the bytes will be accounted
in space_info by the three guys.
space_info->bytes_may_use --- space_info->reserved --- space_info->used.
But on the other hand, in qgroup, there are only two counters to account the
bytes, qgroup->reserved and qgroup->excl. And qg->reserved accounts
bytes in space_info->bytes_may_use and qg->excl accounts bytes in
space_info->used. So the bytes in space_info->reserved is not accounted
in qgroup. If so, there is a window we can exceed the quota limit when
bytes is in space_info->reserved.

Example:
	# btrfs quota enable /mnt
	# btrfs qgroup limit -e 10M /mnt
	# for((i=0;i<20;i++));do fallocate -l 1M /mnt/data$i; done
	# sync
	# btrfs qgroup show -pcre /mnt
qgroupid rfer     excl     max_rfer max_excl parent  child
-------- ----     ----     -------- -------- ------  -----
0/5      20987904 20987904 0        10485760 ---     ---

qg->excl is 20987904 larger than max_excl 10485760.

This patch introduce a new counter named may_use to qgroup, then
there are three counters in qgroup to account bytes in space_info
as below.
space_info->bytes_may_use --- space_info->reserved --- space_info->used.
qgroup->may_use           --- qgroup->reserved     --- qgroup->excl

With this patch applied:
	# btrfs quota enable /mnt
	# btrfs qgroup limit -e 10M /mnt
	# for((i=0;i<20;i++));do fallocate -l 1M /mnt/data$i; done
fallocate: /mnt/data9: fallocate failed: Disk quota exceeded
fallocate: /mnt/data10: fallocate failed: Disk quota exceeded
fallocate: /mnt/data11: fallocate failed: Disk quota exceeded
fallocate: /mnt/data12: fallocate failed: Disk quota exceeded
fallocate: /mnt/data13: fallocate failed: Disk quota exceeded
fallocate: /mnt/data14: fallocate failed: Disk quota exceeded
fallocate: /mnt/data15: fallocate failed: Disk quota exceeded
fallocate: /mnt/data16: fallocate failed: Disk quota exceeded
fallocate: /mnt/data17: fallocate failed: Disk quota exceeded
fallocate: /mnt/data18: fallocate failed: Disk quota exceeded
fallocate: /mnt/data19: fallocate failed: Disk quota exceeded
	# sync
	# btrfs qgroup show -pcre /mnt
qgroupid rfer    excl    max_rfer max_excl parent  child
-------- ----    ----    -------- -------- ------  -----
0/5      9453568 9453568 0        10485760 ---     ---

Reported-by: Cyril SCETBON <cyril.scetbon@free.fr>
Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 6ef97c184c7b..a9f69a0d4b08 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -60,6 +60,7 @@
 #include "backref.h"
 #include "hash.h"
 #include "props.h"
+#include "qgroup.h"
 
 struct btrfs_iget_args {
 	struct btrfs_key *location;
@@ -753,7 +754,9 @@ retry:
 			}
 			goto out_free;
 		}
-
+		btrfs_qgroup_update_reserved_bytes(root->fs_info,
+						   root->root_key.objectid,
+						   ins.offset, 1);
 		/*
 		 * here we're doing allocation and writeback of the
 		 * compressed pages
@@ -978,6 +981,10 @@ static noinline int cow_file_range(struct inode *inode,
 		if (ret < 0)
 			goto out_unlock;
 
+		btrfs_qgroup_update_reserved_bytes(root->fs_info,
+						   root->root_key.objectid,
+						   ins.offset, 1);
+
 		em = alloc_extent_map();
 		if (!em) {
 			ret = -ENOMEM;
@@ -7030,6 +7037,10 @@ static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
 		return ERR_PTR(ret);
 	}
 
+	btrfs_qgroup_update_reserved_bytes(root->fs_info,
+					   root->root_key.objectid,
+					   ins.offset, 1);
+
 	return em;
 }
 
@@ -9583,6 +9594,11 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode,
 				btrfs_end_transaction(trans, root);
 			break;
 		}
+
+		btrfs_qgroup_update_reserved_bytes(root->fs_info,
+						   root->root_key.objectid,
+						   ins.offset, 1);
+
 		btrfs_drop_extent_cache(inode, cur_offset,
 					cur_offset + ins.offset -1, 0);