linux-ext4 - [PATCH v2] ext4: choose hardlimit when softlimit is larger than hardlimit in ext4_statfs

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Date:   Tue, 15 Oct 2019 18:23:27 +0800
From:   Chengguang Xu <cgxu519@...ernel.net>
To:     tytso@....edu, adilger.kernel@...ger.ca, jack@...e.com
Cc:     linux-ext4@...r.kernel.org, Chengguang Xu <cgxu519@...ernel.net>
Subject: [PATCH v2] ext4: choose hardlimit when softlimit is larger than  hardlimit in ext4_statfs_project()

Setting softlimit larger than hardlimit seems meaningless
for disk quota but currently it is allowed. In this case,
there may be a bit of comfusion for users when they run
df comamnd to directory which has project quota.

For example, we set 20M softlimit and 10M hardlimit of
block usage limit for project quota of test_dir(project id 123).

[root@...es mnt_ext4]# repquota -P -a
*** Report for project quotas on device /dev/loop0
Block grace time: 7days; Inode grace time: 7days
                        Block limits                File limits
Project         used    soft    hard  grace    used  soft  hard  grace
----------------------------------------------------------------------
 0        --      13       0       0              2     0     0
 123      --   10237   20480   10240              5   200   100

The result of df command as below:

[root@...es mnt_ext4]# df -h test_dir
Filesystem      Size  Used Avail Use% Mounted on
/dev/loop0       20M   10M   10M  50% /home/cgxu/test/mnt_ext4

Even though it looks like there is another 10M free space to use,
if we write new data to diretory test_dir(inherit project id),
the write will fail with errno(-EDQUOT).

After this patch, the df result looks like below.

[root@...es mnt_ext4]# df -h test_dir
Filesystem      Size  Used Avail Use% Mounted on
/dev/loop0       10M   10M  3.0K 100% /home/cgxu/test/mnt_ext4

Signed-off-by: Chengguang Xu <cgxu519@...ernel.net>
---
- Fix a bug in the limit setting logic.

 fs/ext4/super.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dd654e53ba3d..f24e175ae5e0 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5546,9 +5546,15 @@ static int ext4_statfs_project(struct super_block *sb,
 		return PTR_ERR(dquot);
 	spin_lock(&dquot->dq_dqb_lock);
 
-	limit = (dquot->dq_dqb.dqb_bsoftlimit ?
-		 dquot->dq_dqb.dqb_bsoftlimit :
-		 dquot->dq_dqb.dqb_bhardlimit) >> sb->s_blocksize_bits;
+	limit = 0;
+	if (dquot->dq_dqb.dqb_bsoftlimit &&
+		(!limit || dquot->dq_dqb.dqb_bsoftlimit < limit))
+		limit = dquot->dq_dqb.dqb_bsoftlimit;
+	if (dquot->dq_dqb.dqb_bhardlimit &&
+		(!limit || dquot->dq_dqb.dqb_bhardlimit < limit))
+		limit = dquot->dq_dqb.dqb_bhardlimit;
+	limit >>= sb->s_blocksize_bits;
+
 	if (limit && buf->f_blocks > limit) {
 		curblock = (dquot->dq_dqb.dqb_curspace +
 			    dquot->dq_dqb.dqb_rsvspace) >> sb->s_blocksize_bits;
@@ -5558,9 +5564,14 @@ static int ext4_statfs_project(struct super_block *sb,
 			 (buf->f_blocks - curblock) : 0;
 	}
 
-	limit = dquot->dq_dqb.dqb_isoftlimit ?
-		dquot->dq_dqb.dqb_isoftlimit :
-		dquot->dq_dqb.dqb_ihardlimit;
+	limit = 0;
+	if (dquot->dq_dqb.dqb_isoftlimit &&
+		(!limit || dquot->dq_dqb.dqb_isoftlimit < limit))
+		limit = dquot->dq_dqb.dqb_isoftlimit;
+	if (dquot->dq_dqb.dqb_ihardlimit &&
+		(!limit || dquot->dq_dqb.dqb_ihardlimit < limit))
+		limit = dquot->dq_dqb.dqb_ihardlimit;
+
 	if (limit && buf->f_files > limit) {
 		buf->f_files = limit;
 		buf->f_ffree =
-- 
2.20.1