Add server recovery helpers

Add a little set of functions to help the server track which clients are
waiting to recover which state.  The open map messages need to wait for
recovery so we're moving recovery out of being only in the lock server.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/Makefile

@@ -30,6 +30,7 @@ scoutfs-y +=			\
 	options.o		\
 	per_task.o		\
 	quorum.o		\
+	recov.o			\
 	scoutfs_trace.o		\
 	server.o		\
 	sort_priv.o		\

kmod/src/recov.c

@@ -0,0 +1,280 @@
+/*
+ * Copyright (C) 2021 Versity Software, Inc.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/rhashtable.h>
+#include <linux/rcupdate.h>
+
+#include "super.h"
+#include "recov.h"
+
+/*
+ * There are a few server messages which can't be processed until they
+ * know that they have state for all possibly active clients.  These
+ * little helpers track which clients have recovered what state and give
+ * those message handlers a call to check if recovery has completed.  We
+ * track the timeout here, but all we do is call back into the server to
+ * take steps to evict timed out clients and then let us know that their
+ * recovery has finished.
+ */
+
+struct recov_info {
+	struct super_block *sb;
+	spinlock_t lock;
+	struct list_head pending;
+	struct timer_list timer;
+	void (*timeout_fn)(struct super_block *);
+};
+
+#define DECLARE_RECOV_INFO(sb, name) \
+	struct recov_info *name = SCOUTFS_SB(sb)->recov_info
+
+struct recov_pending {
+	struct list_head head;
+	u64 rid;
+	int which;
+};
+
+static struct recov_pending *find_pending(struct recov_info *recinf, u64 rid, int which)
+{
+	struct recov_pending *pend;
+
+	list_for_each_entry(pend, &recinf->pending, head) {
+		if ((rid == 0 || pend->rid == rid) && (pend->which & which))
+			return pend;
+	}
+
+	return NULL;
+}
+
+/*
+ * Record that we'll be waiting for a client to recover something.
+ * _finished will eventually be called for every _prepare, either
+ * because recovery naturally finished or because it timed out and the
+ * server evicted the client. 
+ */
+int scoutfs_recov_prepare(struct super_block *sb, u64 rid, int which)
+{
+	DECLARE_RECOV_INFO(sb, recinf);
+	struct recov_pending *alloc;
+	struct recov_pending *pend;
+
+	if (WARN_ON_ONCE(which & SCOUTFS_RECOV_INVALID))
+		return -EINVAL;
+
+	alloc = kmalloc(sizeof(*pend), GFP_NOFS);
+	if (!alloc)
+		return -ENOMEM;
+
+	spin_lock(&recinf->lock);
+
+	pend = find_pending(recinf, rid, SCOUTFS_RECOV_ALL);
+	if (pend) {
+		pend->which |= which;
+	} else {
+		swap(pend, alloc);
+		pend->rid = rid;
+		pend->which = which;
+		list_add(&pend->head, &recinf->pending);
+	}
+
+	spin_unlock(&recinf->lock);
+
+	kfree(alloc);
+	return 0;
+}
+
+/*
+ * Recovery is only finished once we've begun (which sets the timer) and
+ * all clients have finished.  If we didn't test the timer we could
+ * claim it finished prematurely as clients are being prepared.
+ */
+static int recov_finished(struct recov_info *recinf)
+{
+	return !!(recinf->timeout_fn != NULL && list_empty(&recinf->pending));
+}
+
+static void timer_callback(struct timer_list *timer)
+{
+	struct recov_info *recinf = from_timer(recinf, timer, timer);
+
+	recinf->timeout_fn(recinf->sb);
+}
+
+/*
+ * Begin waiting for recovery once we've prepared all the clients.  If
+ * the timeout period elapses before _finish is called on all prepared
+ * clients then the timer will call the callback.
+ *
+ * Returns > 0 if all the prepared clients finish recovery before begin
+ * is called.
+ */
+int scoutfs_recov_begin(struct super_block *sb, void (*timeout_fn)(struct super_block *),
+			unsigned int timeout_ms)
+{
+	DECLARE_RECOV_INFO(sb, recinf);
+	int ret;
+
+	spin_lock(&recinf->lock);
+
+	recinf->timeout_fn = timeout_fn;
+	recinf->timer.expires = jiffies + msecs_to_jiffies(timeout_ms);
+	add_timer(&recinf->timer);
+
+	ret = recov_finished(recinf);
+
+	spin_unlock(&recinf->lock);
+
+	if (ret > 0)
+		del_timer_sync(&recinf->timer);
+
+	return ret;
+}
+
+/*
+ * A given client has recovered the given state.  If it's finished all
+ * recovery then we free it, and if all clients have finished recovery
+ * then we cancel the timeout timer.
+ *
+ * Returns > 0 if _begin has been called and all clients have finished.
+ * The caller will only see > 0 returned once.
+ */
+int scoutfs_recov_finish(struct super_block *sb, u64 rid, int which)
+{
+	DECLARE_RECOV_INFO(sb, recinf);
+	struct recov_pending *pend;
+	int ret = 0;
+
+	spin_lock(&recinf->lock);
+
+	pend = find_pending(recinf, rid, which);
+	if (pend) {
+		pend->which &= ~which;
+		if (pend->which) {
+			pend = NULL;
+		} else {
+			list_del(&pend->head);
+			ret = recov_finished(recinf);
+		}
+	}
+
+	spin_unlock(&recinf->lock);
+
+	if (ret > 0)
+		del_timer_sync(&recinf->timer);
+
+	kfree(pend);
+
+	return ret;
+}
+
+/*
+ * Returns true if the given client is still trying to recover
+ * the given state.
+ */
+bool scoutfs_recov_is_pending(struct super_block *sb, u64 rid, int which)
+{
+	DECLARE_RECOV_INFO(sb, recinf);
+	bool is_pending;
+
+	spin_lock(&recinf->lock);
+	is_pending = find_pending(recinf, rid, which) != NULL;
+	spin_unlock(&recinf->lock);
+
+	return is_pending;
+}
+
+/*
+ * Returns 0 if there are no rids waiting for the given state to be
+ * recovered.  Returns the rid of a client still waiting if there are
+ * any, in no specified order.
+ *
+ * This is inherently racey.  Callers are responsible for resolving any
+ * actions taken based on pending with the recovery finishing, perhaps
+ * before we return.
+ */
+u64 scoutfs_recov_next_pending(struct super_block *sb, int which)
+{
+	DECLARE_RECOV_INFO(sb, recinf);
+	struct recov_pending *pend;
+	u64 rid;
+
+	spin_lock(&recinf->lock);
+	pend = find_pending(recinf, 0, which);
+	rid = pend ? pend->rid : 0;
+	spin_unlock(&recinf->lock);
+
+	return rid;
+}
+
+/*
+ * The server is shutting down and doesn't need to worry about recovery
+ * anymore.  It'll be built up again by the next server, if needed.
+ */
+void scoutfs_recov_shutdown(struct super_block *sb)
+{
+	DECLARE_RECOV_INFO(sb, recinf);
+	struct recov_pending *pend;
+	struct recov_pending *tmp;
+	LIST_HEAD(list);
+
+	del_timer_sync(&recinf->timer);
+
+	spin_lock(&recinf->lock);
+	list_splice_init(&recinf->pending, &list);
+	recinf->timeout_fn = NULL;
+	spin_unlock(&recinf->lock);
+
+	list_for_each_entry_safe(pend, tmp, &recinf->pending, head) {
+		list_del(&pend->head);
+		kfree(pend);
+	}
+}
+
+int scoutfs_recov_setup(struct super_block *sb)
+{
+	struct scoutfs_sb_info *sbi = SCOUTFS_SB(sb);
+	struct recov_info *recinf;
+	int ret;
+
+	recinf = kzalloc(sizeof(struct recov_info), GFP_KERNEL);
+	if (!recinf) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	recinf->sb = sb;
+	spin_lock_init(&recinf->lock);
+	INIT_LIST_HEAD(&recinf->pending);
+	timer_setup(&recinf->timer, timer_callback, 0);
+
+	sbi->recov_info = recinf;
+	ret = 0;
+out:
+	return ret;
+}
+
+void scoutfs_recov_destroy(struct super_block *sb)
+{
+	DECLARE_RECOV_INFO(sb, recinf);
+	struct scoutfs_sb_info *sbi = SCOUTFS_SB(sb);
+
+	if (recinf) {
+		scoutfs_recov_shutdown(sb);
+
+		kfree(recinf);
+		sbi->recov_info = NULL;
+	}
+}

kmod/src/recov.h

@@ -0,0 +1,23 @@
+#ifndef _SCOUTFS_RECOV_H_
+#define _SCOUTFS_RECOV_H_
+
+enum {
+	SCOUTFS_RECOV_GREETING	= ( 1 <<  0),
+	SCOUTFS_RECOV_LOCKS	= ( 1 <<  1),
+
+	SCOUTFS_RECOV_INVALID	= (~0 <<  2),
+	SCOUTFS_RECOV_ALL	= (~SCOUTFS_RECOV_INVALID),
+};
+
+int scoutfs_recov_prepare(struct super_block *sb, u64 rid, int which);
+int scoutfs_recov_begin(struct super_block *sb, void (*timeout_fn)(struct super_block *),
+			unsigned int timeout_ms);
+int scoutfs_recov_finish(struct super_block *sb, u64 rid, int which);
+bool scoutfs_recov_is_pending(struct super_block *sb, u64 rid, int which);
+u64 scoutfs_recov_next_pending(struct super_block *sb, int which);
+void scoutfs_recov_shutdown(struct super_block *sb);
+
+int scoutfs_recov_setup(struct super_block *sb);
+void scoutfs_recov_destroy(struct super_block *sb);
+
+#endif

kmod/src/super.h

@@ -26,6 +26,7 @@ struct net_info;
 struct block_info;
 struct forest_info;
 struct srch_info;
+struct recov_info;
 
 struct scoutfs_sb_info {
 	struct super_block *sb;
@@ -70,6 +71,7 @@ struct scoutfs_sb_info {
 	struct lock_server_info *lock_server_info;
 	struct client_info *client_info;
 	struct server_info *server_info;
+	struct recov_info *recov_info;
 	struct sysfs_info *sfsinfo;
 
 	struct scoutfs_counters *counters;