1 files changed, 43 insertions, 11 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index a409312ee0df..c5dc32a59c76 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2240,6 +2240,7 @@ struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
 	}
 	res = d_splice_alias(inode, found);
 	if (res) {
+		d_lookup_done(found);
 		dput(found);
 		return res;
 	}
@@ -2570,7 +2571,15 @@ EXPORT_SYMBOL(d_rehash);
 
 static inline unsigned start_dir_add(struct inode *dir)
 {
-
+	/*
+	 * The caller holds a spinlock (dentry::d_lock). On !PREEMPT_RT
+	 * kernels spin_lock() implicitly disables preemption, but not on
+	 * PREEMPT_RT.  So for RT it has to be done explicitly to protect
+	 * the sequence count write side critical section against a reader
+	 * or another writer preempting, which would result in a live lock.
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		preempt_disable();
 	for (;;) {
 		unsigned n = dir->i_dir_seq;
 		if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
@@ -2579,9 +2588,13 @@ static inline unsigned start_dir_add(struct inode *dir)
 	}
 }
 
-static inline void end_dir_add(struct inode *dir, unsigned n)
+static inline void end_dir_add(struct inode *dir, unsigned int n,
+			       wait_queue_head_t *d_wait)
 {
 	smp_store_release(&dir->i_dir_seq, n + 2);
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		preempt_enable();
+	wake_up_all(d_wait);
 }
 
 static void d_wait_lookup(struct dentry *dentry)
@@ -2708,32 +2721,50 @@ mismatch:
 }
 EXPORT_SYMBOL(d_alloc_parallel);
 
-void __d_lookup_done(struct dentry *dentry)
+/*
+ * - Unhash the dentry
+ * - Retrieve and clear the waitqueue head in dentry
+ * - Return the waitqueue head
+ */
+static wait_queue_head_t *__d_lookup_unhash(struct dentry *dentry)
 {
-	struct hlist_bl_head *b = in_lookup_hash(dentry->d_parent,
-						 dentry->d_name.hash);
+	wait_queue_head_t *d_wait;
+	struct hlist_bl_head *b;
+
+	lockdep_assert_held(&dentry->d_lock);
+
+	b = in_lookup_hash(dentry->d_parent, dentry->d_name.hash);
 	hlist_bl_lock(b);
 	dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
 	__hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
-	wake_up_all(dentry->d_wait);
+	d_wait = dentry->d_wait;
 	dentry->d_wait = NULL;
 	hlist_bl_unlock(b);
 	INIT_HLIST_NODE(&dentry->d_u.d_alias);
 	INIT_LIST_HEAD(&dentry->d_lru);
+	return d_wait;
+}
+
+void __d_lookup_unhash_wake(struct dentry *dentry)
+{
+	spin_lock(&dentry->d_lock);
+	wake_up_all(__d_lookup_unhash(dentry));
+	spin_unlock(&dentry->d_lock);
 }
-EXPORT_SYMBOL(__d_lookup_done);
+EXPORT_SYMBOL(__d_lookup_unhash_wake);
 
 /* inode->i_lock held if inode is non-NULL */
 
 static inline void __d_add(struct dentry *dentry, struct inode *inode)
 {
+	wait_queue_head_t *d_wait;
 	struct inode *dir = NULL;
 	unsigned n;
 	spin_lock(&dentry->d_lock);
 	if (unlikely(d_in_lookup(dentry))) {
 		dir = dentry->d_parent->d_inode;
 		n = start_dir_add(dir);
-		__d_lookup_done(dentry);
+		d_wait = __d_lookup_unhash(dentry);
 	}
 	if (inode) {
 		unsigned add_flags = d_flags_for_inode(inode);
@@ -2745,7 +2776,7 @@ static inline void __d_add(struct dentry *dentry, struct inode *inode)
 	}
 	__d_rehash(dentry);
 	if (dir)
-		end_dir_add(dir, n);
+		end_dir_add(dir, n, d_wait);
 	spin_unlock(&dentry->d_lock);
 	if (inode)
 		spin_unlock(&inode->i_lock);
@@ -2892,6 +2923,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
 		     bool exchange)
 {
 	struct dentry *old_parent, *p;
+	wait_queue_head_t *d_wait;
 	struct inode *dir = NULL;
 	unsigned n;
 
@@ -2922,7 +2954,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
 	if (unlikely(d_in_lookup(target))) {
 		dir = target->d_parent->d_inode;
 		n = start_dir_add(dir);
-		__d_lookup_done(target);
+		d_wait = __d_lookup_unhash(target);
 	}
 
 	write_seqcount_begin(&dentry->d_seq);
@@ -2958,7 +2990,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
 	write_seqcount_end(&dentry->d_seq);
 
 	if (dir)
-		end_dir_add(dir, n);
+		end_dir_add(dir, n, d_wait);
 
 	if (dentry->d_parent != old_parent)
 		spin_unlock(&dentry->d_parent->d_lock);