plock.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2005-2008 Red Hat, Inc.  All rights reserved.
 */

#include <linux/fs.h>
#include <linux/filelock.h>
#include <linux/miscdevice.h>
#include <linux/poll.h>
#include <linux/dlm.h>
#include <linux/dlm_plock.h>
#include <linux/slab.h>

#include <trace/events/dlm.h>

#include "dlm_internal.h"
#include "lockspace.h"

static DEFINE_SPINLOCK(ops_lock);
static LIST_HEAD(send_list);
static LIST_HEAD(recv_list);
static DECLARE_WAIT_QUEUE_HEAD(send_wq);
static DECLARE_WAIT_QUEUE_HEAD(recv_wq);

struct plock_async_data {
	void *fl;
	void *file;
	struct file_lock flc;
	int (*callback)(struct file_lock *fl, int result);
};

struct plock_op {
	struct list_head list;
	int done;
	struct dlm_plock_info info;
	/* if set indicates async handling */
	struct plock_async_data *data;
};

static inline void set_version(struct dlm_plock_info *info)
{
	info->version[0] = DLM_PLOCK_VERSION_MAJOR;
	info->version[1] = DLM_PLOCK_VERSION_MINOR;
	info->version[2] = DLM_PLOCK_VERSION_PATCH;
}

static struct plock_op *plock_lookup_waiter(const struct dlm_plock_info *info)
{
	struct plock_op *op = NULL, *iter;

	list_for_each_entry(iter, &recv_list, list) {
		if (iter->info.fsid == info->fsid &&
		    iter->info.number == info->number &&
		    iter->info.owner == info->owner &&
		    iter->info.pid == info->pid &&
		    iter->info.start == info->start &&
		    iter->info.end == info->end &&
		    iter->info.ex == info->ex &&
		    iter->info.wait) {
			op = iter;
			break;
		}
	}

	return op;
}

static int check_version(struct dlm_plock_info *info)
{
	if ((DLM_PLOCK_VERSION_MAJOR != info->version[0]) ||
	    (DLM_PLOCK_VERSION_MINOR < info->version[1])) {
		log_print("plock device version mismatch: "
			  "kernel (%u.%u.%u), user (%u.%u.%u)",
			  DLM_PLOCK_VERSION_MAJOR,
			  DLM_PLOCK_VERSION_MINOR,
			  DLM_PLOCK_VERSION_PATCH,
			  info->version[0],
			  info->version[1],
			  info->version[2]);
		return -EINVAL;
	}
	return 0;
}

static void dlm_release_plock_op(struct plock_op *op)
{
	kfree(op->data);
	kfree(op);
}

static void send_op(struct plock_op *op)
{
	set_version(&op->info);
	spin_lock(&ops_lock);
	list_add_tail(&op->list, &send_list);
	spin_unlock(&ops_lock);
	wake_up(&send_wq);
}

static int do_lock_cancel(const struct dlm_plock_info *orig_info)
{
	struct plock_op *op;
	int rv;

	op = kzalloc(sizeof(*op), GFP_NOFS);
	if (!op)
		return -ENOMEM;

	op->info = *orig_info;
	op->info.optype = DLM_PLOCK_OP_CANCEL;
	op->info.wait = 0;

	send_op(op);
	wait_event(recv_wq, (op->done != 0));

	rv = op->info.rv;

	dlm_release_plock_op(op);
	return rv;
}

int dlm_posix_lock(dlm_lockspace_t *lockspace, u64 number, struct file *file,
		   int cmd, struct file_lock *fl)
{
	struct plock_async_data *op_data;
	struct dlm_ls *ls;
	struct plock_op *op;
	int rv;

	ls = dlm_find_lockspace_local(lockspace);
	if (!ls)
		return -EINVAL;

	op = kzalloc(sizeof(*op), GFP_NOFS);
	if (!op) {
		rv = -ENOMEM;
		goto out;
	}

	op->info.optype		= DLM_PLOCK_OP_LOCK;
	op->info.pid		= fl->c.flc_pid;
	op->info.ex		= lock_is_write(fl);
	op->info.wait		= !!(fl->c.flc_flags & FL_SLEEP);
	op->info.fsid		= ls->ls_global_id;
	op->info.number		= number;
	op->info.start		= fl->fl_start;
	op->info.end		= fl->fl_end;
	op->info.owner = (__u64)(long) fl->c.flc_owner;
	/* async handling */
	if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
		op_data = kzalloc(sizeof(*op_data), GFP_NOFS);
		if (!op_data) {
			dlm_release_plock_op(op);
			rv = -ENOMEM;
			goto out;
		}

		op_data->callback = fl->fl_lmops->lm_grant;
		locks_init_lock(&op_data->flc);
		locks_copy_lock(&op_data->flc, fl);
		op_data->fl		= fl;
		op_data->file	= file;

		op->data = op_data;

		send_op(op);
		rv = FILE_LOCK_DEFERRED;
		goto out;
	}

	send_op(op);

	if (op->info.wait) {
		rv = wait_event_interruptible(recv_wq, (op->done != 0));
		if (rv == -ERESTARTSYS) {
			spin_lock(&ops_lock);
			/* recheck under ops_lock if we got a done != 0,
			 * if so this interrupt case should be ignored
			 */
			if (op->done != 0) {
				spin_unlock(&ops_lock);
				goto do_lock_wait;
			}
			spin_unlock(&ops_lock);

			rv = do_lock_cancel(&op->info);
			switch (rv) {
			case 0:
				/* waiter was deleted in user space, answer will never come
				 * remove original request. The original request must be
				 * on recv_list because the answer of do_lock_cancel()
				 * synchronized it.
				 */
				spin_lock(&ops_lock);
				list_del(&op->list);
				spin_unlock(&ops_lock);
				rv = -EINTR;
				break;
			case -ENOENT:
				/* cancellation wasn't successful but op should be done */
				fallthrough;
			default:
				/* internal error doing cancel we need to wait */
				goto wait;
			}

			log_debug(ls, "%s: wait interrupted %x %llx pid %d",
				  __func__, ls->ls_global_id,
				  (unsigned long long)number, op->info.pid);
			dlm_release_plock_op(op);
			goto out;
		}
	} else {
wait:
		wait_event(recv_wq, (op->done != 0));
	}

do_lock_wait:

	WARN_ON(!list_empty(&op->list));

	rv = op->info.rv;

	if (!rv) {
		if (locks_lock_file_wait(file, fl) < 0)
			log_error(ls, "dlm_posix_lock: vfs lock error %llx",
				  (unsigned long long)number);
	}

	dlm_release_plock_op(op);
out:
	dlm_put_lockspace(ls);
	return rv;
}
EXPORT_SYMBOL_GPL(dlm_posix_lock);

/* Returns failure iff a successful lock operation should be canceled */
static int dlm_plock_callback(struct plock_op *op)
{
	struct plock_async_data *op_data = op->data;
	struct file *file;
	struct file_lock *fl;
	struct file_lock *flc;
	int (*notify)(struct file_lock *fl, int result) = NULL;
	int rv = 0;

	WARN_ON(!list_empty(&op->list));

	/* check if the following 2 are still valid or make a copy */
	file = op_data->file;
	flc = &op_data->flc;
	fl = op_data->fl;
	notify = op_data->callback;

	if (op->info.rv) {
		notify(fl, op->info.rv);
		goto out;
	}

	/* got fs lock; bookkeep locally as well: */
	flc->c.flc_flags &= ~FL_SLEEP;
	if (posix_lock_file(file, flc, NULL)) {
		/*
		 * This can only happen in the case of kmalloc() failure.
		 * The filesystem's own lock is the authoritative lock,
		 * so a failure to get the lock locally is not a disaster.
		 * As long as the fs cannot reliably cancel locks (especially
		 * in a low-memory situation), we're better off ignoring
		 * this failure than trying to recover.
		 */
		log_print("dlm_plock_callback: vfs lock error %llx file %p fl %p",
			  (unsigned long long)op->info.number, file, fl);
	}

	rv = notify(fl, 0);
	if (rv) {
		/* XXX: We need to cancel the fs lock here: */
		log_print("%s: lock granted after lock request failed; dangling lock!",
			  __func__);
		goto out;
	}

out:
	dlm_release_plock_op(op);
	return rv;
}

int dlm_posix_unlock(dlm_lockspace_t *lockspace, u64 number, struct file *file,
		     struct file_lock *fl)
{
	struct dlm_ls *ls;
	struct plock_op *op;
	int rv;
	unsigned char saved_flags = fl->c.flc_flags;

	ls = dlm_find_lockspace_local(lockspace);
	if (!ls)
		return -EINVAL;

	op = kzalloc(sizeof(*op), GFP_NOFS);
	if (!op) {
		rv = -ENOMEM;
		goto out;
	}

	/* cause the vfs unlock to return ENOENT if lock is not found */
	fl->c.flc_flags |= FL_EXISTS;

	rv = locks_lock_file_wait(file, fl);
	if (rv == -ENOENT) {
		rv = 0;
		goto out_free;
	}
	if (rv < 0) {
		log_error(ls, "dlm_posix_unlock: vfs unlock error %d %llx",
			  rv, (unsigned long long)number);
	}

	op->info.optype		= DLM_PLOCK_OP_UNLOCK;
	op->info.pid		= fl->c.flc_pid;
	op->info.fsid		= ls->ls_global_id;
	op->info.number		= number;
	op->info.start		= fl->fl_start;
	op->info.end		= fl->fl_end;
	op->info.owner = (__u64)(long) fl->c.flc_owner;

	if (fl->c.flc_flags & FL_CLOSE) {
		op->info.flags |= DLM_PLOCK_FL_CLOSE;
		send_op(op);
		rv = 0;
		goto out;
	}

	send_op(op);
	wait_event(recv_wq, (op->done != 0));

	WARN_ON(!list_empty(&op->list));

	rv = op->info.rv;

	if (rv == -ENOENT)
		rv = 0;

out_free:
	dlm_release_plock_op(op);
out:
	dlm_put_lockspace(ls);
	fl->c.flc_flags = saved_flags;
	return rv;
}
EXPORT_SYMBOL_GPL(dlm_posix_unlock);

/*
 * NOTE: This implementation can only handle async lock requests as nfs
 * do it. It cannot handle cancellation of a pending lock request sitting
 * in wait_event(), but for now only nfs is the only user local kernel
 * user.
 */
int dlm_posix_cancel(dlm_lockspace_t *lockspace, u64 number, struct file *file,
		     struct file_lock *fl)
{
	struct dlm_plock_info info;
	struct plock_op *op;
	struct dlm_ls *ls;
	int rv;

	/* this only works for async request for now and nfs is the only
	 * kernel user right now.
	 */
	if (WARN_ON_ONCE(!fl->fl_lmops || !fl->fl_lmops->lm_grant))
		return -EOPNOTSUPP;

	ls = dlm_find_lockspace_local(lockspace);
	if (!ls)
		return -EINVAL;

	memset(&info, 0, sizeof(info));
	info.pid = fl->c.flc_pid;
	info.ex = lock_is_write(fl);
	info.fsid = ls->ls_global_id;
	dlm_put_lockspace(ls);
	info.number = number;
	info.start = fl->fl_start;
	info.end = fl->fl_end;
	info.owner = (__u64)(long) fl->c.flc_owner;

	rv = do_lock_cancel(&info);
	switch (rv) {
	case 0:
		spin_lock(&ops_lock);
		/* lock request to cancel must be on recv_list because
		 * do_lock_cancel() synchronizes it.
		 */
		op = plock_lookup_waiter(&info);
		if (WARN_ON_ONCE(!op)) {
			spin_unlock(&ops_lock);
			rv = -ENOLCK;
			break;
		}

		list_del(&op->list);
		spin_unlock(&ops_lock);
		WARN_ON(op->info.optype != DLM_PLOCK_OP_LOCK);
		op->data->callback(op->data->fl, -EINTR);
		dlm_release_plock_op(op);
		rv = -EINTR;
		break;
	case -ENOENT:
		/* if cancel wasn't successful we probably were to late
		 * or it was a non-blocking lock request, so just unlock it.
		 */
		rv = dlm_posix_unlock(lockspace, number, file, fl);
		break;
	default:
		break;
	}

	return rv;
}
EXPORT_SYMBOL_GPL(dlm_posix_cancel);

int dlm_posix_get(dlm_lockspace_t *lockspace, u64 number, struct file *file,
		  struct file_lock *fl)
{
	struct dlm_ls *ls;
	struct plock_op *op;
	int rv;

	ls = dlm_find_lockspace_local(lockspace);
	if (!ls)
		return -EINVAL;

	op = kzalloc(sizeof(*op), GFP_NOFS);
	if (!op) {
		rv = -ENOMEM;
		goto out;
	}

	op->info.optype		= DLM_PLOCK_OP_GET;
	op->info.pid		= fl->c.flc_pid;
	op->info.ex		= lock_is_write(fl);
	op->info.fsid		= ls->ls_global_id;
	op->info.number		= number;
	op->info.start		= fl->fl_start;
	op->info.end		= fl->fl_end;
	op->info.owner = (__u64)(long) fl->c.flc_owner;

	send_op(op);
	wait_event(recv_wq, (op->done != 0));

	WARN_ON(!list_empty(&op->list));

	/* info.rv from userspace is 1 for conflict, 0 for no-conflict,
	   -ENOENT if there are no locks on the file */

	rv = op->info.rv;

	fl->c.flc_type = F_UNLCK;
	if (rv == -ENOENT)
		rv = 0;
	else if (rv > 0) {
		locks_init_lock(fl);
		fl->c.flc_type = (op->info.ex) ? F_WRLCK : F_RDLCK;
		fl->c.flc_flags = FL_POSIX;
		fl->c.flc_pid = op->info.pid;
		if (op->info.nodeid != dlm_our_nodeid())
			fl->c.flc_pid = -fl->c.flc_pid;
		fl->fl_start = op->info.start;
		fl->fl_end = op->info.end;
		rv = 0;
	}

	dlm_release_plock_op(op);
out:
	dlm_put_lockspace(ls);
	return rv;
}
EXPORT_SYMBOL_GPL(dlm_posix_get);

/* a read copies out one plock request from the send list */
static ssize_t dev_read(struct file *file, char __user *u, size_t count,
			loff_t *ppos)
{
	struct dlm_plock_info info;
	struct plock_op *op = NULL;

	if (count < sizeof(info))
		return -EINVAL;

	spin_lock(&ops_lock);
	if (!list_empty(&send_list)) {
		op = list_first_entry(&send_list, struct plock_op, list);
		if (op->info.flags & DLM_PLOCK_FL_CLOSE)
			list_del(&op->list);
		else
			list_move_tail(&op->list, &recv_list);
		memcpy(&info, &op->info, sizeof(info));
	}
	spin_unlock(&ops_lock);

	if (!op)
		return -EAGAIN;

	trace_dlm_plock_read(&info);

	/* there is no need to get a reply from userspace for unlocks
	   that were generated by the vfs cleaning up for a close
	   (the process did not make an unlock call). */

	if (op->info.flags & DLM_PLOCK_FL_CLOSE)
		dlm_release_plock_op(op);

	if (copy_to_user(u, &info, sizeof(info)))
		return -EFAULT;
	return sizeof(info);
}

/* a write copies in one plock result that should match a plock_op
   on the recv list */
static ssize_t dev_write(struct file *file, const char __user *u, size_t count,
			 loff_t *ppos)
{
	struct plock_op *op = NULL, *iter;
	struct dlm_plock_info info;
	int do_callback = 0;

	if (count != sizeof(info))
		return -EINVAL;

	if (copy_from_user(&info, u, sizeof(info)))
		return -EFAULT;

	trace_dlm_plock_write(&info);

	if (check_version(&info))
		return -EINVAL;

	/*
	 * The results for waiting ops (SETLKW) can be returned in any
	 * order, so match all fields to find the op.  The results for
	 * non-waiting ops are returned in the order that they were sent
	 * to userspace, so match the result with the first non-waiting op.
	 */
	spin_lock(&ops_lock);
	if (info.wait) {
		op = plock_lookup_waiter(&info);
	} else {
		list_for_each_entry(iter, &recv_list, list) {
			if (!iter->info.wait &&
			    iter->info.fsid == info.fsid) {
				op = iter;
				break;
			}
		}
	}

	if (op) {
		/* Sanity check that op and info match. */
		if (info.wait)
			WARN_ON(op->info.optype != DLM_PLOCK_OP_LOCK);
		else
			WARN_ON(op->info.number != info.number ||
				op->info.owner != info.owner ||
				op->info.optype != info.optype);

		list_del_init(&op->list);
		memcpy(&op->info, &info, sizeof(info));
		if (op->data)
			do_callback = 1;
		else
			op->done = 1;
	}
	spin_unlock(&ops_lock);

	if (op) {
		if (do_callback)
			dlm_plock_callback(op);
		else
			wake_up(&recv_wq);
	} else
		pr_debug("%s: no op %x %llx", __func__,
			 info.fsid, (unsigned long long)info.number);
	return count;
}

static __poll_t dev_poll(struct file *file, poll_table *wait)
{
	__poll_t mask = 0;

	poll_wait(file, &send_wq, wait);

	spin_lock(&ops_lock);
	if (!list_empty(&send_list))
		mask = EPOLLIN | EPOLLRDNORM;
	spin_unlock(&ops_lock);

	return mask;
}

static const struct file_operations dev_fops = {
	.read    = dev_read,
	.write   = dev_write,
	.poll    = dev_poll,
	.owner   = THIS_MODULE,
	.llseek  = noop_llseek,
};

static struct miscdevice plock_dev_misc = {
	.minor = MISC_DYNAMIC_MINOR,
	.name = DLM_PLOCK_MISC_NAME,
	.fops = &dev_fops
};

int dlm_plock_init(void)
{
	int rv;

	rv = misc_register(&plock_dev_misc);
	if (rv)
		log_print("dlm_plock_init: misc_register failed %d", rv);
	return rv;
}

void dlm_plock_exit(void)
{
	misc_deregister(&plock_dev_misc);
	WARN_ON(!list_empty(&send_list));
	WARN_ON(!list_empty(&recv_list));
}