NFSv4: Fix up stateid locking...

We really don't need to grab both the state->so_owner and the
inode->i_lock.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4_fs.h

@@ -139,9 +139,11 @@ struct nfs4_state {
 	unsigned long flags;		/* Do we hold any locks? */
 	spinlock_t state_lock;		/* Protects the lock_states list */
 
+	seqlock_t seqlock;		/* Protects the stateid/open_stateid */
 	nfs4_stateid stateid;		/* Current stateid: may be delegation */
 	nfs4_stateid open_stateid;	/* OPEN stateid */
 
+	/* The following 3 fields are protected by owner->so_lock */
 	unsigned int n_rdonly;		/* Number of read-only references */
 	unsigned int n_wronly;		/* Number of write-only references */
 	unsigned int n_rdwr;		/* Number of read/write references */

fs/nfs/nfs4proc.c

@@ -385,29 +385,28 @@ static void nfs_set_open_stateid_locked(struct nfs4_state *state, nfs4_stateid *
 
 static void nfs_set_open_stateid(struct nfs4_state *state, nfs4_stateid *stateid, int open_flags)
 {
-	spin_lock(&state->owner->so_lock);
-	spin_lock(&state->inode->i_lock);
+	write_seqlock(&state->seqlock);
 	nfs_set_open_stateid_locked(state, stateid, open_flags);
-	spin_unlock(&state->inode->i_lock);
-	spin_unlock(&state->owner->so_lock);
+	write_sequnlock(&state->seqlock);
 }
 
 static void update_open_stateid(struct nfs4_state *state, nfs4_stateid *open_stateid, nfs4_stateid *deleg_stateid, int open_flags)
 {
-	struct inode *inode = state->inode;
-
 	open_flags &= (FMODE_READ|FMODE_WRITE);
-	/* Protect against nfs4_find_state_byowner() */
-	spin_lock(&state->owner->so_lock);
-	spin_lock(&inode->i_lock);
+	/*
+	 * Protect the call to nfs4_state_set_mode_locked and
+	 * serialise the stateid update
+	 */
+	write_seqlock(&state->seqlock);
 	if (deleg_stateid != NULL) {
 		memcpy(state->stateid.data, deleg_stateid->data, sizeof(state->stateid.data));
 		set_bit(NFS_DELEGATED_STATE, &state->flags);
 	}
 	if (open_stateid != NULL)
 		nfs_set_open_stateid_locked(state, open_stateid, open_flags);
+	write_sequnlock(&state->seqlock);
+	spin_lock(&state->owner->so_lock);
 	update_open_stateflags(state, open_flags);
-	spin_unlock(&inode->i_lock);
 	spin_unlock(&state->owner->so_lock);
 }
 
@@ -608,12 +607,10 @@ static int nfs4_open_recover(struct nfs4_opendata *opendata, struct nfs4_state *
 	 */
 	if (test_bit(NFS_DELEGATED_STATE, &state->flags) == 0 &&
 	    memcmp(state->stateid.data, state->open_stateid.data, sizeof(state->stateid.data)) != 0) {
-		spin_lock(&state->owner->so_lock);
-		spin_lock(&state->inode->i_lock);
+		write_seqlock(&state->seqlock);
 		if (test_bit(NFS_DELEGATED_STATE, &state->flags) == 0)
 			memcpy(state->stateid.data, state->open_stateid.data, sizeof(state->stateid.data));
-		spin_unlock(&state->inode->i_lock);
-		spin_unlock(&state->owner->so_lock);
+		write_sequnlock(&state->seqlock);
 	}
 	return 0;
 }
@@ -1280,7 +1277,6 @@ static void nfs4_close_prepare(struct rpc_task *task, void *data)
 	mode = FMODE_READ|FMODE_WRITE;
 	clear_rd = clear_wr = clear_rdwr = 0;
 	spin_lock(&state->owner->so_lock);
-	spin_lock(&calldata->inode->i_lock);
 	/* Calculate the change in open mode */
 	if (state->n_rdwr == 0) {
 		if (state->n_rdonly == 0) {
@@ -1294,7 +1290,6 @@ static void nfs4_close_prepare(struct rpc_task *task, void *data)
 			clear_rdwr |= test_and_clear_bit(NFS_O_RDWR_STATE, &state->flags);
 		}
 	}
-	spin_unlock(&calldata->inode->i_lock);
 	spin_unlock(&state->owner->so_lock);
 	if (!clear_rd && !clear_wr && !clear_rdwr) {
 		/* Note: exit _without_ calling nfs4_close_done */

fs/nfs/nfs4state.c

@@ -307,6 +307,7 @@ nfs4_alloc_open_state(void)
 	atomic_set(&state->count, 1);
 	INIT_LIST_HEAD(&state->lock_states);
 	spin_lock_init(&state->state_lock);
+	seqlock_init(&state->seqlock);
 	return state;
 }
 
@@ -411,7 +412,6 @@ void nfs4_put_open_state(struct nfs4_state *state)
  */
 void nfs4_close_state(struct path *path, struct nfs4_state *state, mode_t mode)
 {
-	struct inode *inode = state->inode;
 	struct nfs4_state_owner *owner = state->owner;
 	int call_close = 0;
 	int newstate;
@@ -419,7 +419,6 @@ void nfs4_close_state(struct path *path, struct nfs4_state *state, mode_t mode)
 	atomic_inc(&owner->so_count);
 	/* Protect against nfs4_find_state() */
 	spin_lock(&owner->so_lock);
-	spin_lock(&inode->i_lock);
 	switch (mode & (FMODE_READ | FMODE_WRITE)) {
 		case FMODE_READ:
 			state->n_rdonly--;
@@ -446,7 +445,6 @@ void nfs4_close_state(struct path *path, struct nfs4_state *state, mode_t mode)
 			clear_bit(NFS_DELEGATED_STATE, &state->flags);
 	}
 	nfs4_state_set_mode_locked(state, newstate);
-	spin_unlock(&inode->i_lock);
 	spin_unlock(&owner->so_lock);
 
 	if (!call_close) {
@@ -599,8 +597,12 @@ int nfs4_set_lock_state(struct nfs4_state *state, struct file_lock *fl)
 void nfs4_copy_stateid(nfs4_stateid *dst, struct nfs4_state *state, fl_owner_t fl_owner)
 {
 	struct nfs4_lock_state *lsp;
+	int seq;
 
-	memcpy(dst, &state->stateid, sizeof(*dst));
+	do {
+		seq = read_seqbegin(&state->seqlock);
+		memcpy(dst, &state->stateid, sizeof(*dst));
+	} while (read_seqretry(&state->seqlock, seq));
 	if (test_bit(LK_STATE_IN_USE, &state->flags) == 0)
 		return;