1 files changed, 78 insertions, 18 deletions

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 88aa747f4800..c7afe433d991 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -225,13 +225,22 @@ static void put_quota_format(struct quota_format_type *fmt)
 
 /*
  * Dquot List Management:
- * The quota code uses four lists for dquot management: the inuse_list,
- * free_dquots, dqi_dirty_list, and dquot_hash[] array. A single dquot
- * structure may be on some of those lists, depending on its current state.
+ * The quota code uses five lists for dquot management: the inuse_list,
+ * releasing_dquots, free_dquots, dqi_dirty_list, and dquot_hash[] array.
+ * A single dquot structure may be on some of those lists, depending on
+ * its current state.
  *
  * All dquots are placed to the end of inuse_list when first created, and this
  * list is used for invalidate operation, which must look at every dquot.
  *
+ * When the last reference of a dquot will be dropped, the dquot will be
+ * added to releasing_dquots. We'd then queue work item which would call
+ * synchronize_srcu() and after that perform the final cleanup of all the
+ * dquots on the list. Both releasing_dquots and free_dquots use the
+ * dq_free list_head in the dquot struct. When a dquot is removed from
+ * releasing_dquots, a reference count is always subtracted, and if
+ * dq_count == 0 at that point, the dquot will be added to the free_dquots.
+ *
  * Unused dquots (dq_count == 0) are added to the free_dquots list when freed,
  * and this list is searched whenever we need an available dquot.  Dquots are
  * removed from the list as soon as they are used again, and
@@ -250,6 +259,7 @@ static void put_quota_format(struct quota_format_type *fmt)
 
 static LIST_HEAD(inuse_list);
 static LIST_HEAD(free_dquots);
+static LIST_HEAD(releasing_dquots);
 static unsigned int dq_hash_bits, dq_hash_mask;
 static struct hlist_head *dquot_hash;
 
@@ -260,6 +270,9 @@ static qsize_t inode_get_rsv_space(struct inode *inode);
 static qsize_t __inode_get_rsv_space(struct inode *inode);
 static int __dquot_initialize(struct inode *inode, int type);
 
+static void quota_release_workfn(struct work_struct *work);
+static DECLARE_DELAYED_WORK(quota_release_work, quota_release_workfn);
+
 static inline unsigned int
 hashfn(const struct super_block *sb, struct kqid qid)
 {
@@ -305,12 +318,18 @@ static inline void put_dquot_last(struct dquot *dquot)
 	dqstats_inc(DQST_FREE_DQUOTS);
 }
 
+static inline void put_releasing_dquots(struct dquot *dquot)
+{
+	list_add_tail(&dquot->dq_free, &releasing_dquots);
+}
+
 static inline void remove_free_dquot(struct dquot *dquot)
 {
 	if (list_empty(&dquot->dq_free))
 		return;
 	list_del_init(&dquot->dq_free);
-	dqstats_dec(DQST_FREE_DQUOTS);
+	if (!atomic_read(&dquot->dq_count))
+		dqstats_dec(DQST_FREE_DQUOTS);
 }
 
 static inline void put_inuse(struct dquot *dquot)
@@ -552,6 +571,8 @@ static void invalidate_dquots(struct super_block *sb, int type)
 	struct dquot *dquot, *tmp;
 
 restart:
+	flush_delayed_work(&quota_release_work);
+
 	spin_lock(&dq_list_lock);
 	list_for_each_entry_safe(dquot, tmp, &inuse_list, dq_inuse) {
 		if (dquot->dq_sb != sb)
@@ -560,6 +581,12 @@ restart:
 			continue;
 		/* Wait for dquot users */
 		if (atomic_read(&dquot->dq_count)) {
+			/* dquot in releasing_dquots, flush and retry */
+			if (!list_empty(&dquot->dq_free)) {
+				spin_unlock(&dq_list_lock);
+				goto restart;
+			}
+
 			atomic_inc(&dquot->dq_count);
 			spin_unlock(&dq_list_lock);
 			/*
@@ -771,6 +798,49 @@ static struct shrinker dqcache_shrinker = {
 };
 
 /*
+ * Safely release dquot and put reference to dquot.
+ */
+static void quota_release_workfn(struct work_struct *work)
+{
+	struct dquot *dquot;
+	struct list_head rls_head;
+
+	spin_lock(&dq_list_lock);
+	/* Exchange the list head to avoid livelock. */
+	list_replace_init(&releasing_dquots, &rls_head);
+	spin_unlock(&dq_list_lock);
+
+restart:
+	synchronize_srcu(&dquot_srcu);
+	spin_lock(&dq_list_lock);
+	while (!list_empty(&rls_head)) {
+		dquot = list_first_entry(&rls_head, struct dquot, dq_free);
+		/* Dquot got used again? */
+		if (atomic_read(&dquot->dq_count) > 1) {
+			remove_free_dquot(dquot);
+			atomic_dec(&dquot->dq_count);
+			continue;
+		}
+		if (dquot_dirty(dquot)) {
+			spin_unlock(&dq_list_lock);
+			/* Commit dquot before releasing */
+			dquot_write_dquot(dquot);
+			goto restart;
+		}
+		if (dquot_active(dquot)) {
+			spin_unlock(&dq_list_lock);
+			dquot->dq_sb->dq_op->release_dquot(dquot);
+			goto restart;
+		}
+		/* Dquot is inactive and clean, now move it to free list */
+		remove_free_dquot(dquot);
+		atomic_dec(&dquot->dq_count);
+		put_dquot_last(dquot);
+	}
+	spin_unlock(&dq_list_lock);
+}
+
+/*
  * Put reference to dquot
  */
 void dqput(struct dquot *dquot)
@@ -786,7 +856,7 @@ void dqput(struct dquot *dquot)
 	}
 #endif
 	dqstats_inc(DQST_DROPS);
-we_slept:
+
 	spin_lock(&dq_list_lock);
 	if (atomic_read(&dquot->dq_count) > 1) {
 		/* We have more than one user... nothing to do */
@@ -798,25 +868,15 @@ we_slept:
 		spin_unlock(&dq_list_lock);
 		return;
 	}
+
 	/* Need to release dquot? */
-	if (dquot_dirty(dquot)) {
-		spin_unlock(&dq_list_lock);
-		/* Commit dquot before releasing */
-		dquot_write_dquot(dquot);
-		goto we_slept;
-	}
-	if (dquot_active(dquot)) {
-		spin_unlock(&dq_list_lock);
-		dquot->dq_sb->dq_op->release_dquot(dquot);
-		goto we_slept;
-	}
-	atomic_dec(&dquot->dq_count);
 #ifdef CONFIG_QUOTA_DEBUG
 	/* sanity check */
 	BUG_ON(!list_empty(&dquot->dq_free));
 #endif
-	put_dquot_last(dquot);
+	put_releasing_dquots(dquot);
 	spin_unlock(&dq_list_lock);
+	queue_delayed_work(system_unbound_wq, &quota_release_work, 1);
 }
 EXPORT_SYMBOL(dqput);