nfs: allow blocking locks to be awoken by lock callbacks

Add a waitqueue head to the client structure. Have clients set a wait
on that queue prior to requesting a lock from the server. If the lock
is blocked, then we can use that to wait for wakeups.

Note that we do need to do this "manually" since we need to set the
wait on the waitqueue prior to requesting the lock, but requesting a
lock can involve activities that can block.

However, only do that for NFSv4.1 locks, either by compiling out
all of the waitqueue handling when CONFIG_NFS_V4_1 is disabled, or
skipping all of it at runtime if we're dealing with v4.0, or v4.1
servers that don't send lock callbacks.

Note too that even when we expect to get a lock callback, RFC5661
section 20.11.4 is pretty clear that we still need to poll for them,
so we do still sleep on a timeout. We do however always poll at the
longest interval in that case.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
[Anna: nfs4_retry_setlk() "status" should default to -ERESTARTSYS]
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/callback_proc.c

@@ -638,6 +638,10 @@ __be32 nfs4_callback_notify_lock(struct cb_notify_lock_args *args, void *dummy,
 	dprintk_rcu("NFS: CB_NOTIFY_LOCK request from %s\n",
 		rpc_peeraddr2str(cps->clp->cl_rpcclient, RPC_DISPLAY_ADDR));
 
+	/* Don't wake anybody if the string looked bogus */
+	if (args->cbnl_valid)
+		__wake_up(&cps->clp->cl_lock_waitq, TASK_NORMAL, 0, args);
+
 	return htonl(NFS4_OK);
 }
 #endif /* CONFIG_NFS_V4_1 */

fs/nfs/nfs4client.c

@@ -199,6 +199,9 @@ struct nfs_client *nfs4_alloc_client(const struct nfs_client_initdata *cl_init)
 	clp->cl_minorversion = cl_init->minorversion;
 	clp->cl_mvops = nfs_v4_minor_ops[cl_init->minorversion];
 	clp->cl_mig_gen = 1;
+#if IS_ENABLED(CONFIG_NFS_V4_1)
+	init_waitqueue_head(&clp->cl_lock_waitq);
+#endif
 	return clp;
 
 error:

fs/nfs/nfs4proc.c

@@ -6166,7 +6166,8 @@ static int nfs4_proc_setlk(struct nfs4_state *state, int cmd, struct file_lock *
 #define NFS4_LOCK_MAXTIMEOUT (30 * HZ)
 
 static int
-nfs4_retry_setlk(struct nfs4_state *state, int cmd, struct file_lock *request)
+nfs4_retry_setlk_simple(struct nfs4_state *state, int cmd,
+			struct file_lock *request)
 {
 	int		status = -ERESTARTSYS;
 	unsigned long	timeout = NFS4_LOCK_MINTIMEOUT;
@@ -6183,6 +6184,97 @@ nfs4_retry_setlk(struct nfs4_state *state, int cmd, struct file_lock *request)
 	return status;
 }
 
+#ifdef CONFIG_NFS_V4_1
+struct nfs4_lock_waiter {
+	struct task_struct	*task;
+	struct inode		*inode;
+	struct nfs_lowner	*owner;
+	bool			notified;
+};
+
+static int
+nfs4_wake_lock_waiter(wait_queue_t *wait, unsigned int mode, int flags, void *key)
+{
+	int ret;
+	struct cb_notify_lock_args *cbnl = key;
+	struct nfs4_lock_waiter	*waiter	= wait->private;
+	struct nfs_lowner	*lowner = &cbnl->cbnl_owner,
+				*wowner = waiter->owner;
+
+	/* Only wake if the callback was for the same owner */
+	if (lowner->clientid != wowner->clientid ||
+	    lowner->id != wowner->id		 ||
+	    lowner->s_dev != wowner->s_dev)
+		return 0;
+
+	/* Make sure it's for the right inode */
+	if (nfs_compare_fh(NFS_FH(waiter->inode), &cbnl->cbnl_fh))
+		return 0;
+
+	waiter->notified = true;
+
+	/* override "private" so we can use default_wake_function */
+	wait->private = waiter->task;
+	ret = autoremove_wake_function(wait, mode, flags, key);
+	wait->private = waiter;
+	return ret;
+}
+
+static int
+nfs4_retry_setlk(struct nfs4_state *state, int cmd, struct file_lock *request)
+{
+	int status = -ERESTARTSYS;
+	unsigned long flags;
+	struct nfs4_lock_state *lsp = request->fl_u.nfs4_fl.owner;
+	struct nfs_server *server = NFS_SERVER(state->inode);
+	struct nfs_client *clp = server->nfs_client;
+	wait_queue_head_t *q = &clp->cl_lock_waitq;
+	struct nfs_lowner owner = { .clientid = clp->cl_clientid,
+				    .id = lsp->ls_seqid.owner_id,
+				    .s_dev = server->s_dev };
+	struct nfs4_lock_waiter waiter = { .task  = current,
+					   .inode = state->inode,
+					   .owner = &owner,
+					   .notified = false };
+	wait_queue_t wait;
+
+	/* Don't bother with waitqueue if we don't expect a callback */
+	if (!test_bit(NFS_STATE_MAY_NOTIFY_LOCK, &state->flags))
+		return nfs4_retry_setlk_simple(state, cmd, request);
+
+	init_wait(&wait);
+	wait.private = &waiter;
+	wait.func = nfs4_wake_lock_waiter;
+	add_wait_queue(q, &wait);
+
+	while(!signalled()) {
+		status = nfs4_proc_setlk(state, cmd, request);
+		if ((status != -EAGAIN) || IS_SETLK(cmd))
+			break;
+
+		status = -ERESTARTSYS;
+		spin_lock_irqsave(&q->lock, flags);
+		if (waiter.notified) {
+			spin_unlock_irqrestore(&q->lock, flags);
+			continue;
+		}
+		set_current_state(TASK_INTERRUPTIBLE);
+		spin_unlock_irqrestore(&q->lock, flags);
+
+		freezable_schedule_timeout_interruptible(NFS4_LOCK_MAXTIMEOUT);
+	}
+
+	finish_wait(q, &wait);
+	return status;
+}
+#else /* !CONFIG_NFS_V4_1 */
+static inline int
+nfs4_retry_setlk(struct nfs4_state *state, int cmd, struct file_lock *request)
+{
+	return nfs4_retry_setlk_simple(state, cmd, request);
+}
+#endif
+
 static int
 nfs4_proc_lock(struct file *filp, int cmd, struct file_lock *request)
 {

include/linux/nfs_fs_sb.h

@@ -103,6 +103,9 @@ struct nfs_client {
 #define NFS_SP4_MACH_CRED_WRITE    5	/* WRITE */
 #define NFS_SP4_MACH_CRED_COMMIT   6	/* COMMIT */
 #define NFS_SP4_MACH_CRED_PNFS_CLEANUP  7 /* LAYOUTRETURN */
+#if IS_ENABLED(CONFIG_NFS_V4_1)
+	wait_queue_head_t	cl_lock_waitq;
+#endif /* CONFIG_NFS_V4_1 */
 #endif /* CONFIG_NFS_V4 */
 
 	/* Our own IP address, as a null-terminated string.