quota: Allow negative usage of space and inodes

For clustered filesystems, it can happen that space / inode usage goes
negative temporarily (because some node is allocating another node
is freeing and they are not completely in sync). So let quota code
allow this and change qsize_t so a signed type so that we don't
underflow the variables.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

2 files changed, 6 insertions, 3 deletions

diff --git a/fs/dquot.c b/fs/dquot.c
index 74185c34a4f0..9c78ffe1aad2 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -847,7 +847,8 @@ static inline void dquot_incr_space(struct dquot *dquot, qsize_t number)
 
 static inline void dquot_decr_inodes(struct dquot *dquot, qsize_t number)
 {
-        if (dquot->dq_dqb.dqb_curinodes > number)
+        if (sb_dqopt(dquot->dq_sb)->flags & DQUOT_NEGATIVE_USAGE ||
+            dquot->dq_dqb.dqb_curinodes >= number)
                 dquot->dq_dqb.dqb_curinodes -= number;
         else
                 dquot->dq_dqb.dqb_curinodes = 0;
@@ -858,7 +859,8 @@ static inline void dquot_decr_inodes(struct dquot *dquot, qsize_t number)
 
 static inline void dquot_decr_space(struct dquot *dquot, qsize_t number)
 {
-        if (dquot->dq_dqb.dqb_curspace > number)
+        if (sb_dqopt(dquot->dq_sb)->flags & DQUOT_NEGATIVE_USAGE ||
+            dquot->dq_dqb.dqb_curspace >= number)
                 dquot->dq_dqb.dqb_curspace -= number;
         else
                 dquot->dq_dqb.dqb_curspace = 0;
diff --git a/include/linux/quota.h b/include/linux/quota.h
index e51dfdc0aef0..75bf761caef2 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -168,7 +168,7 @@ enum {
 #include <asm/atomic.h>
 
 typedef __kernel_uid32_t qid_t; /* Type in which we store ids in memory */
-typedef __u64 qsize_t;          /* Type in which we store sizes */
+typedef long long qsize_t;      /* Type in which we store sizes */
 
 extern spinlock_t dq_data_lock;
 
@@ -336,6 +336,7 @@ enum {
                                                  * responsible for setting
                                                  * S_NOQUOTA, S_NOATIME flags
                                                  */
+#define DQUOT_NEGATIVE_USAGE    (1 << 7)        /* Allow negative quota usage */
 
 static inline unsigned int dquot_state_flag(unsigned int flags, int type)
 {