[PATCH 1/2] btrfs: Add WARN_ON for qgroup reserved underflow

[Qu Wenruo]

While the reason why qgroup reserved space may underflow is still under
investigation, such WARN_ON will help us to expose the bug more easily,
and for end-user we can detect and avoid underflow.

Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
---
 fs/btrfs/qgroup.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 8db2e29..8532587 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1061,8 +1061,12 @@ static int __qgroup_excl_accounting(struct btrfs_fs_info 
*fs_info,
        WARN_ON(sign < 0 && qgroup->excl < num_bytes);
        qgroup->excl += sign * num_bytes;
        qgroup->excl_cmpr += sign * num_bytes;
-       if (sign > 0)
-               qgroup->reserved -= num_bytes;
+       if (sign > 0) {
+               if (WARN_ON(qgroup->reserved < num_bytes))
+                       qgroup->reserved = 0;
+               else
+                       qgroup->reserved -= num_bytes;
+       }
 
        qgroup_dirty(fs_info, qgroup);
 
@@ -1082,8 +1086,12 @@ static int __qgroup_excl_accounting(struct btrfs_fs_info 
*fs_info,
                qgroup->rfer_cmpr += sign * num_bytes;
                WARN_ON(sign < 0 && qgroup->excl < num_bytes);
                qgroup->excl += sign * num_bytes;
-               if (sign > 0)
-                       qgroup->reserved -= num_bytes;
+               if (sign > 0) {
+                       if (WARN_ON(qgroup->reserved < num_bytes))
+                               qgroup->reserved = 0;
+                       else
+                               qgroup->reserved -= num_bytes;
+               }
                qgroup->excl_cmpr += sign * num_bytes;
                qgroup_dirty(fs_info, qgroup);
 
@@ -2201,7 +2209,10 @@ void btrfs_qgroup_free_refroot(struct btrfs_fs_info 
*fs_info,
 
                qg = u64_to_ptr(unode->aux);
 
-               qg->reserved -= num_bytes;
+               if (WARN_ON(qgroup->reserved < num_bytes))
+                       qgroup->reserved = 0;
+               else
+                       qgroup->reserved -= num_bytes;
 
                list_for_each_entry(glist, &qg->groups, next_group) {
                        ret = ulist_add(fs_info->qgroup_ulist,
-- 
2.10.0



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