fix several lockdep splats, allow multiple splats

index 6af210a..14c44ec 100644
@@ -323,6 +323,15 @@ static inline struct task_group *task_group(struct task_struct *p)
 /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
 static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 {
+	/*
+	 * Strictly speaking this rcu_read_lock() is not needed since the
+	 * task_group is tied to the cgroup, which in turn can never go away
+	 * as long as there are tasks attached to it.
+	 *
+	 * However since task_group() uses task_subsys_state() which is an
+	 * rcu_dereference() user, this quiets CONFIG_PROVE_RCU.
+	 */
+	rcu_read_lock();
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
 	p->se.parent = task_group(p)->se[cpu];

@@ -332,6 +341,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 	p->rt.rt_rq  = task_group(p)->rt_rq[cpu];
 	p->rt.parent = task_group(p)->rt_se[cpu];
 #endif
+	rcu_read_unlock();
 }
 
 #else

index de0bd26..3c2a54f 100644
@@ -323,6 +323,15 @@ static inline struct task_group *task_group(struct task_struct *p)
 /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
 static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 {
+	/*
+	 * Strictly speaking this rcu_read_lock() is not needed since the
+	 * task_group is tied to the cgroup, which in turn can never go away
+	 * as long as there are tasks attached to it.
+	 *
+	 * However since task_group() uses task_subsys_state() which is an
+	 * rcu_dereference() user, this quiets CONFIG_PROVE_RCU.
+	 */
+	rcu_read_lock();
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
 	p->se.parent = task_group(p)->se[cpu];

@@ -332,6 +341,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 	p->rt.rt_rq  = task_group(p)->rt_rq[cpu];
 	p->rt.parent = task_group(p)->rt_se[cpu];
 #endif
+	rcu_read_unlock();
 }
 
 #else

index da5e139..e5c0244 100644
@@ -205,9 +205,12 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
 	 * No lock is needed, since the task isn't on tasklist yet,
 	 * so it can't be moved to another cgroup, which means the
 	 * freezer won't be removed and will be valid during this
-	 * function call.
+	 * function call.  Nevertheless, apply RCU read-side critical
+	 * section to suppress RCU lockdep false positives.
 	 */
+	rcu_read_lock();
 	freezer = task_freezer(task);
+	rcu_read_unlock();
 
 	/*
 	 * The root cgroup is non-freezable, so we can skip the

index da5e139..e5c0244 100644
@@ -205,9 +205,12 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
 	 * No lock is needed, since the task isn't on tasklist yet,
 	 * so it can't be moved to another cgroup, which means the
 	 * freezer won't be removed and will be valid during this
-	 * function call.
+	 * function call.  Nevertheless, apply RCU read-side critical
+	 * section to suppress RCU lockdep false positives.
 	 */
+	rcu_read_lock();
 	freezer = task_freezer(task);
+	rcu_read_unlock();
 
 	/*
 	 * The root cgroup is non-freezable, so we can skip the

index 07db2fe..ec9ab49 100644
@@ -190,6 +190,15 @@ static inline int rcu_read_lock_sched_held(void)
 
 #ifdef CONFIG_PROVE_RCU
 
+#define __do_rcu_dereference_check(c)					\
+	do {								\
+		static bool __warned;					\
+		if (debug_lockdep_rcu_enabled() && !__warned && !(c)) {	\
+			__warned = true;				\
+			lockdep_rcu_dereference(__FILE__, __LINE__);	\
+		}							\
+	} while (0)
+
 /**
  * rcu_dereference_check - rcu_dereference with debug checking
  * @p: The pointer to read, prior to dereferencing

@@ -219,8 +228,7 @@ static inline int rcu_read_lock_sched_held(void)
  */
 #define rcu_dereference_check(p, c) \
 	({ \
-		if (debug_lockdep_rcu_enabled() && !(c)) \
-			lockdep_rcu_dereference(__FILE__, __LINE__); \
+		__do_rcu_dereference_check(c); \
 		rcu_dereference_raw(p); \
 	})
 

@@ -237,8 +245,7 @@ static inline int rcu_read_lock_sched_held(void)
  */
 #define rcu_dereference_protected(p, c) \
 	({ \
-		if (debug_lockdep_rcu_enabled() && !(c)) \
-			lockdep_rcu_dereference(__FILE__, __LINE__); \
+		__do_rcu_dereference_check(c); \
 		(p); \
 	})
 

index 2594e1c..03dd1fa 100644
@@ -3801,8 +3801,6 @@ void lockdep_rcu_dereference(const char *file, const int line)
 {
 	struct task_struct *curr = current;
 
-	if (!debug_locks_off())
-		return;
 	printk("\n===================================================\n");
 	printk(  "[ INFO: suspicious rcu_dereference_check() usage. ]\n");
 	printk(  "---------------------------------------------------\n");

index 1567124..8d9ec49 100644
@@ -129,21 +129,35 @@ again:
  */
 void nfs_inode_reclaim_delegation(struct inode *inode, struct rpc_cred *cred, struct nfs_openres *res)
 {
-	struct nfs_delegation *delegation = NFS_I(inode)->delegation;
-	struct rpc_cred *oldcred;
+	struct nfs_delegation *delegation;
+	struct rpc_cred *oldcred = NULL;
 
-	if (delegation == NULL)
-		return;
-	memcpy(delegation->stateid.data, res->delegation.data,
-			sizeof(delegation->stateid.data));
-	delegation->type = res->delegation_type;
-	delegation->maxsize = res->maxsize;
-	oldcred = delegation->cred;
-	delegation->cred = get_rpccred(cred);
-	clear_bit(NFS_DELEGATION_NEED_RECLAIM, &delegation->flags);
-	NFS_I(inode)->delegation_state = delegation->type;
-	smp_wmb();
-	put_rpccred(oldcred);
+	rcu_read_lock();
+	delegation = rcu_dereference(NFS_I(inode)->delegation);
+	if (delegation != NULL) {
+		spin_lock(&delegation->lock);
+		if (delegation->inode != NULL) {
+			memcpy(delegation->stateid.data, res->delegation.data,
+			       sizeof(delegation->stateid.data));
+			delegation->type = res->delegation_type;
+			delegation->maxsize = res->maxsize;
+			oldcred = delegation->cred;
+			delegation->cred = get_rpccred(cred);
+			clear_bit(NFS_DELEGATION_NEED_RECLAIM,
+				  &delegation->flags);
+			NFS_I(inode)->delegation_state = delegation->type;
+			spin_unlock(&delegation->lock);
+			put_rpccred(oldcred);
+			rcu_read_unlock();
+		} else {
+			/* We appear to have raced with a delegation return. */
+			spin_unlock(&delegation->lock);
+			rcu_read_unlock();
+			nfs_inode_set_delegation(inode, cred, res);
+		}
+	} else {
+		rcu_read_unlock();
+	}
 }
 
 static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation, int issync)

index 8d9ec49..ea61d26 100644
@@ -24,6 +24,8 @@
 
 static void nfs_do_free_delegation(struct nfs_delegation *delegation)
 {
+	if (delegation->cred)
+		put_rpccred(delegation->cred);
 	kfree(delegation);
 }
 

@@ -36,13 +38,7 @@ static void nfs_free_delegation_callback(struct rcu_head *head)
 
 static void nfs_free_delegation(struct nfs_delegation *delegation)
 {
-	struct rpc_cred *cred;
-
-	cred = rcu_dereference(delegation->cred);
-	rcu_assign_pointer(delegation->cred, NULL);
 	call_rcu(&delegation->rcu, nfs_free_delegation_callback);
-	if (cred)
-		put_rpccred(cred);
 }
 
 void nfs_mark_delegation_referenced(struct nfs_delegation *delegation)

@@ -180,9 +176,13 @@ static struct inode *nfs_delegation_grab_inode(struct nfs_delegation *delegation
 	return inode;
 }
 
-static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi, const nfs4_stateid *stateid)
+static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi,
+							   const nfs4_stateid *stateid,
+							   struct nfs_client *clp)
 {
-	struct nfs_delegation *delegation = rcu_dereference(nfsi->delegation);
+	struct nfs_delegation *delegation =
+		rcu_dereference_protected(nfsi->delegation,
+					  lockdep_is_held(&clp->cl_lock));
 
 	if (delegation == NULL)
 		goto nomatch;

@@ -209,7 +209,7 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
 {
 	struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
 	struct nfs_inode *nfsi = NFS_I(inode);
-	struct nfs_delegation *delegation;
+	struct nfs_delegation *delegation, *old_delegation;
 	struct nfs_delegation *freeme = NULL;
 	int status = 0;
 

@@ -227,10 +227,12 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
 	spin_lock_init(&delegation->lock);
 
 	spin_lock(&clp->cl_lock);
-	if (rcu_dereference(nfsi->delegation) != NULL) {
-		if (memcmp(&delegation->stateid, &nfsi->delegation->stateid,
-					sizeof(delegation->stateid)) == 0 &&
-				delegation->type == nfsi->delegation->type) {
+	old_delegation = rcu_dereference_protected(nfsi->delegation,
+						   lockdep_is_held(&clp->cl_lock));
+	if (old_delegation != NULL) {
+		if (memcmp(&delegation->stateid, &old_delegation->stateid,
+					sizeof(old_delegation->stateid)) == 0 &&
+				delegation->type == old_delegation->type) {
 			goto out;
 		}
 		/*

@@ -240,12 +242,12 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
 		dfprintk(FILE, "%s: server %s handed out "
 				"a duplicate delegation!\n",
 				__func__, clp->cl_hostname);
-		if (delegation->type <= nfsi->delegation->type) {
+		if (delegation->type <= old_delegation->type) {
 			freeme = delegation;
 			delegation = NULL;
 			goto out;
 		}
-		freeme = nfs_detach_delegation_locked(nfsi, NULL);
+		freeme = nfs_detach_delegation_locked(nfsi, NULL, clp);
 	}
 	list_add_rcu(&delegation->super_list, &clp->cl_delegations);
 	nfsi->delegation_state = delegation->type;

@@ -315,7 +317,7 @@ restart:
 		if (inode == NULL)
 			continue;
 		spin_lock(&clp->cl_lock);
-		delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL);
+		delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL, clp);
 		spin_unlock(&clp->cl_lock);
 		rcu_read_unlock();
 		if (delegation != NULL) {

@@ -344,9 +346,9 @@ void nfs_inode_return_delegation_noreclaim(struct inode *inode)
 	struct nfs_inode *nfsi = NFS_I(inode);
 	struct nfs_delegation *delegation;
 
-	if (rcu_dereference(nfsi->delegation) != NULL) {
+	if (rcu_access_pointer(nfsi->delegation) != NULL) {
 		spin_lock(&clp->cl_lock);
-		delegation = nfs_detach_delegation_locked(nfsi, NULL);
+		delegation = nfs_detach_delegation_locked(nfsi, NULL, clp);
 		spin_unlock(&clp->cl_lock);
 		if (delegation != NULL)
 			nfs_do_return_delegation(inode, delegation, 0);

@@ -360,9 +362,9 @@ int nfs_inode_return_delegation(struct inode *inode)
 	struct nfs_delegation *delegation;
 	int err = 0;
 
-	if (rcu_dereference(nfsi->delegation) != NULL) {
+	if (rcu_access_pointer(nfsi->delegation) != NULL) {
 		spin_lock(&clp->cl_lock);
-		delegation = nfs_detach_delegation_locked(nfsi, NULL);
+		delegation = nfs_detach_delegation_locked(nfsi, NULL, clp);
 		spin_unlock(&clp->cl_lock);
 		if (delegation != NULL) {
 			nfs_msync_inode(inode);

@@ -540,7 +542,7 @@ restart:
 		if (inode == NULL)
 			continue;
 		spin_lock(&clp->cl_lock);
-		delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL);
+		delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL, clp);
 		spin_unlock(&clp->cl_lock);
 		rcu_read_unlock();
 		if (delegation != NULL)