clntlock.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * linux/fs/lockd/clntlock.c
 *
 * Lock handling for the client side NLM implementation
 *
 * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/nfs_fs.h>
#include <linux/sunrpc/addr.h>
#include <linux/sunrpc/svc.h>
#include <linux/lockd/lockd.h>
#include <linux/kthread.h>

#define NLMDBG_FACILITY		NLMDBG_CLIENT

/*
 * Local function prototypes
 */
static int			reclaimer(void *ptr);

/*
 * The following functions handle blocking and granting from the
 * client perspective.
 */

/*
 * This is the representation of a blocked client lock.
 */
struct nlm_wait {
	struct list_head	b_list;		/* linked list */
	wait_queue_head_t	b_wait;		/* where to wait on */
	struct nlm_host *	b_host;
	struct file_lock *	b_lock;		/* local file lock */
	unsigned short		b_reclaim;	/* got to reclaim lock */
	__be32			b_status;	/* grant callback status */
};

static LIST_HEAD(nlm_blocked);
static DEFINE_SPINLOCK(nlm_blocked_lock);

/**
 * nlmclnt_init - Set up per-NFS mount point lockd data structures
 * @nlm_init: pointer to arguments structure
 *
 * Returns pointer to an appropriate nlm_host struct,
 * or an ERR_PTR value.
 */
struct nlm_host *nlmclnt_init(const struct nlmclnt_initdata *nlm_init)
{
	struct nlm_host *host;
	u32 nlm_version = (nlm_init->nfs_version == 2) ? 1 : 4;
	int status;

	status = lockd_up(nlm_init->net, nlm_init->cred);
	if (status < 0)
		return ERR_PTR(status);

	host = nlmclnt_lookup_host(nlm_init->address, nlm_init->addrlen,
				   nlm_init->protocol, nlm_version,
				   nlm_init->hostname, nlm_init->noresvport,
				   nlm_init->net, nlm_init->cred);
	if (host == NULL)
		goto out_nohost;
	if (host->h_rpcclnt == NULL && nlm_bind_host(host) == NULL)
		goto out_nobind;

	host->h_nlmclnt_ops = nlm_init->nlmclnt_ops;
	return host;
out_nobind:
	nlmclnt_release_host(host);
out_nohost:
	lockd_down(nlm_init->net);
	return ERR_PTR(-ENOLCK);
}
EXPORT_SYMBOL_GPL(nlmclnt_init);

/**
 * nlmclnt_done - Release resources allocated by nlmclnt_init()
 * @host: nlm_host structure reserved by nlmclnt_init()
 *
 */
void nlmclnt_done(struct nlm_host *host)
{
	struct net *net = host->net;

	nlmclnt_release_host(host);
	lockd_down(net);
}
EXPORT_SYMBOL_GPL(nlmclnt_done);

/*
 * Queue up a lock for blocking so that the GRANTED request can see it
 */
struct nlm_wait *nlmclnt_prepare_block(struct nlm_host *host, struct file_lock *fl)
{
	struct nlm_wait *block;

	block = kmalloc(sizeof(*block), GFP_KERNEL);
	if (block != NULL) {
		block->b_host = host;
		block->b_lock = fl;
		init_waitqueue_head(&block->b_wait);
		block->b_status = nlm_lck_blocked;

		spin_lock(&nlm_blocked_lock);
		list_add(&block->b_list, &nlm_blocked);
		spin_unlock(&nlm_blocked_lock);
	}
	return block;
}

void nlmclnt_finish_block(struct nlm_wait *block)
{
	if (block == NULL)
		return;
	spin_lock(&nlm_blocked_lock);
	list_del(&block->b_list);
	spin_unlock(&nlm_blocked_lock);
	kfree(block);
}

/*
 * Block on a lock
 */
int nlmclnt_block(struct nlm_wait *block, struct nlm_rqst *req, long timeout)
{
	long ret;

	/* A borken server might ask us to block even if we didn't
	 * request it. Just say no!
	 */
	if (block == NULL)
		return -EAGAIN;

	/* Go to sleep waiting for GRANT callback. Some servers seem
	 * to lose callbacks, however, so we're going to poll from
	 * time to time just to make sure.
	 *
	 * For now, the retry frequency is pretty high; normally 
	 * a 1 minute timeout would do. See the comment before
	 * nlmclnt_lock for an explanation.
	 */
	ret = wait_event_interruptible_timeout(block->b_wait,
			block->b_status != nlm_lck_blocked,
			timeout);
	if (ret < 0)
		return -ERESTARTSYS;
	/* Reset the lock status after a server reboot so we resend */
	if (block->b_status == nlm_lck_denied_grace_period)
		block->b_status = nlm_lck_blocked;
	req->a_res.status = block->b_status;
	return 0;
}

/*
 * The server lockd has called us back to tell us the lock was granted
 */
__be32 nlmclnt_grant(const struct sockaddr *addr, const struct nlm_lock *lock)
{
	const struct file_lock *fl = &lock->fl;
	const struct nfs_fh *fh = &lock->fh;
	struct nlm_wait	*block;
	__be32 res = nlm_lck_denied;

	/*
	 * Look up blocked request based on arguments. 
	 * Warning: must not use cookie to match it!
	 */
	spin_lock(&nlm_blocked_lock);
	list_for_each_entry(block, &nlm_blocked, b_list) {
		struct file_lock *fl_blocked = block->b_lock;

		if (fl_blocked->fl_start != fl->fl_start)
			continue;
		if (fl_blocked->fl_end != fl->fl_end)
			continue;
		/*
		 * Careful! The NLM server will return the 32-bit "pid" that
		 * we put on the wire: in this case the lockowner "pid".
		 */
		if (fl_blocked->fl_u.nfs_fl.owner->pid != lock->svid)
			continue;
		if (!rpc_cmp_addr(nlm_addr(block->b_host), addr))
			continue;
		if (nfs_compare_fh(NFS_FH(locks_inode(fl_blocked->fl_file)), fh) != 0)
			continue;
		/* Alright, we found a lock. Set the return status
		 * and wake up the caller
		 */
		block->b_status = nlm_granted;
		wake_up(&block->b_wait);
		res = nlm_granted;
	}
	spin_unlock(&nlm_blocked_lock);
	return res;
}

/*
 * The following procedures deal with the recovery of locks after a
 * server crash.
 */

/*
 * Reclaim all locks on server host. We do this by spawning a separate
 * reclaimer thread.
 */
void
nlmclnt_recovery(struct nlm_host *host)
{
	struct task_struct *task;

	if (!host->h_reclaiming++) {
		nlm_get_host(host);
		task = kthread_run(reclaimer, host, "%s-reclaim", host->h_name);
		if (IS_ERR(task))
			printk(KERN_ERR "lockd: unable to spawn reclaimer "
				"thread. Locks for %s won't be reclaimed! "
				"(%ld)\n", host->h_name, PTR_ERR(task));
	}
}

static int
reclaimer(void *ptr)
{
	struct nlm_host	  *host = (struct nlm_host *) ptr;
	struct nlm_wait	  *block;
	struct nlm_rqst   *req;
	struct file_lock *fl, *next;
	u32 nsmstate;
	struct net *net = host->net;

	req = kmalloc(sizeof(*req), GFP_KERNEL);
	if (!req)
		return 0;

	allow_signal(SIGKILL);

	down_write(&host->h_rwsem);
	lockd_up(net, NULL);	/* note: this cannot fail as lockd is already running */

	dprintk("lockd: reclaiming locks for host %s\n", host->h_name);

restart:
	nsmstate = host->h_nsmstate;

	/* Force a portmap getport - the peer's lockd will
	 * most likely end up on a different port.
	 */
	host->h_nextrebind = jiffies;
	nlm_rebind_host(host);

	/* First, reclaim all locks that have been granted. */
	list_splice_init(&host->h_granted, &host->h_reclaim);
	list_for_each_entry_safe(fl, next, &host->h_reclaim, fl_u.nfs_fl.list) {
		list_del_init(&fl->fl_u.nfs_fl.list);

		/*
		 * sending this thread a SIGKILL will result in any unreclaimed
		 * locks being removed from the h_granted list. This means that
		 * the kernel will not attempt to reclaim them again if a new
		 * reclaimer thread is spawned for this host.
		 */
		if (signalled())
			continue;
		if (nlmclnt_reclaim(host, fl, req) != 0)
			continue;
		list_add_tail(&fl->fl_u.nfs_fl.list, &host->h_granted);
		if (host->h_nsmstate != nsmstate) {
			/* Argh! The server rebooted again! */
			goto restart;
		}
	}

	host->h_reclaiming = 0;
	up_write(&host->h_rwsem);
	dprintk("NLM: done reclaiming locks for host %s\n", host->h_name);

	/* Now, wake up all processes that sleep on a blocked lock */
	spin_lock(&nlm_blocked_lock);
	list_for_each_entry(block, &nlm_blocked, b_list) {
		if (block->b_host == host) {
			block->b_status = nlm_lck_denied_grace_period;
			wake_up(&block->b_wait);
		}
	}
	spin_unlock(&nlm_blocked_lock);

	/* Release host handle after use */
	nlmclnt_release_host(host);
	lockd_down(net);
	kfree(req);
	return 0;
}