[PATCH] make file leases work as they should

This patch fixes the following problems in the file lease:
	when there are multiple shared leases on a file, all the
		lease holders get notified when someone opens the
		file for writing (used to be only the first).
	when a nonblocking open breaks a lease, it will time out
		as it should (used to never time out).

This should make the leases code more usable (hopefully).

fs/locks.c

@@ -119,6 +119,7 @@
 #include <linux/smp_lock.h>
 #include <linux/init.h>
 #include <linux/capability.h>
+#include <linux/timer.h>
 #include <linux/time.h>
 #include <linux/fs.h>
 
@@ -1020,6 +1021,46 @@ int posix_lock_file(struct file *filp, struct file_lock *caller,
 	return error;
 }
 
+/* We already had a lease on this file; just change its type */
+static int lease_modify(struct file_lock **before, int arg)
+{
+	struct file_lock *fl = *before;
+	int error = assign_type(fl, arg);
+
+	if (error)
+		return error;
+	locks_wake_up_blocks(fl);
+	if (arg == F_UNLCK) {
+		struct file *filp = fl->fl_file;
+
+		filp->f_owner.pid = 0;
+		filp->f_owner.uid = 0;
+		filp->f_owner.euid = 0;
+		filp->f_owner.signum = 0;
+		locks_delete_lock(before);
+	}
+	return 0;
+}
+
+static void time_out_leases(struct inode *inode)
+{
+	struct file_lock **before;
+	struct file_lock *fl;
+
+	before = &inode->i_flock;
+	while ((fl = *before) && IS_LEASE(fl) && (fl->fl_type & F_INPROGRESS)) {
+		if ((fl->fl_break_time == 0)
+				|| time_before(jiffies, fl->fl_break_time)) {
+			before = &fl->fl_next;
+			continue;
+		}
+		printk(KERN_INFO "lease broken - owner pid = %d\n", fl->fl_pid);
+		lease_modify(before, fl->fl_type & ~F_INPROGRESS);
+		if (fl == *before)	/* lease_modify may have freed fl */
+			before = &fl->fl_next;
+	}
+}
+
 /**
  *	__get_lease	-	revoke all outstanding leases on file
  *	@inode: the inode of the file to return
@@ -1036,34 +1077,30 @@ int __get_lease(struct inode *inode, unsigned int mode)
 	struct file_lock *new_fl, *flock;
 	struct file_lock *fl;
 	int alloc_err;
+	unsigned long break_time;
+	int i_have_this_lease = 0;
 
-	alloc_err = lease_alloc(NULL, 0, &new_fl);
+	alloc_err = lease_alloc(NULL, mode & FMODE_WRITE ? F_WRLCK : F_RDLCK,
+			&new_fl);
 
 	lock_kernel();
+
+	time_out_leases(inode);
+
 	flock = inode->i_flock;
-	if (flock->fl_type & F_INPROGRESS) {
-		if ((mode & O_NONBLOCK)
-		    || (flock->fl_owner == current->files)) {
-			error = -EWOULDBLOCK;
-			goto out;
-		}
-		if (alloc_err != 0) {
-			error = alloc_err;
-			goto out;
-		}
-		do {
-			error = locks_block_on(flock, new_fl);
-			if (error != 0)
-				goto out;
-			flock = inode->i_flock;
-			if (!(flock && IS_LEASE(flock)))
+	if ((flock == NULL) || !IS_LEASE(flock))
 		goto out;
-		} while (flock->fl_type & F_INPROGRESS);
-	}
+
+	for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next)
+		if (fl->fl_owner == current->files)
+			i_have_this_lease = 1;
 
 	if (mode & FMODE_WRITE) {
 		/* If we want write access, we have to revoke any lease. */
 		future = F_UNLCK | F_INPROGRESS;
+	} else if (flock->fl_type & F_INPROGRESS) {
+		/* If the lease is already being broken, we just leave it */
+		future = flock->fl_type;
 	} else if (flock->fl_type & F_WRLCK) {
 		/* Downgrade the exclusive lease to a read-only lease. */
 		future = F_RDLCK | F_INPROGRESS;
@@ -1072,38 +1109,48 @@ int __get_lease(struct inode *inode, unsigned int mode)
 		goto out;
 	}
 
-	if (alloc_err && (flock->fl_owner != current->files)) {
+	if (alloc_err && !i_have_this_lease && ((mode & O_NONBLOCK) == 0)) {
 		error = alloc_err;
 		goto out;
 	}
 
-	fl = flock;
-	do {
-		fl->fl_type = future;
-		fl = fl->fl_next;
-	} while (fl != NULL && IS_LEASE(fl));
+	break_time = 0;
+	if (lease_break_time > 0) {
+		break_time = jiffies + lease_break_time * HZ;
+		if (break_time == 0)
+			break_time++;	/* so that 0 means no break time */
+	}
 
-	kill_fasync(&flock->fl_fasync, SIGIO, POLL_MSG);
+	for (fl = flock; fl && IS_LEASE(fl); fl = fl->fl_next) {
+		if (fl->fl_type != future) {
+			fl->fl_type = future;
+			fl->fl_break_time = break_time;
+			kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
+		}
+	}
 
-	if ((mode & O_NONBLOCK) || (flock->fl_owner == current->files)) {
+	if (i_have_this_lease || (mode & O_NONBLOCK)) {
 		error = -EWOULDBLOCK;
 		goto out;
 	}
 
-	if (lease_break_time > 0)
-		error = lease_break_time * HZ;
-	else
-		error = 0;
 restart:
-	error = locks_block_on_timeout(flock, new_fl, error);
-	if (error == 0) {
-		/* We timed out.  Unilaterally break the lease. */
-		locks_delete_lock(&inode->i_flock);
-		printk(KERN_WARNING "lease timed out\n");
-	} else if (error > 0) {
-		flock = inode->i_flock;
-		if (flock && IS_LEASE(flock))
+	break_time = flock->fl_break_time;
+	if (break_time != 0) {
+		break_time -= jiffies;
+		if (break_time == 0)
+			break_time++;
+	}
+	error = locks_block_on_timeout(flock, new_fl, break_time);
+	if (error >= 0) {
+		if (error == 0)
+			time_out_leases(inode);
+		/* Wait for the next lease that has not been broken yet */
+		for (flock = inode->i_flock; flock && IS_LEASE(flock);
+				flock = flock->fl_next) {
+			if (flock->fl_type & F_INPROGRESS)
 				goto restart;
+		}
 		error = 0;
 	}
 
@@ -1135,45 +1182,40 @@ time_t lease_get_mtime(struct inode *inode)
  *	@filp: the file
  *
  *	The value returned by this function will be one of
+ *	(if no lease break is pending):
  *
- *	%F_RDLCK to indicate a read-only (type II) lease is held.
+ *	%F_RDLCK to indicate a shared lease is held.
  *
  *	%F_WRLCK to indicate an exclusive lease is held.
  *
- *	XXX: sfr & i disagree over whether F_INPROGRESS
+ *	%F_UNLCK to indicate no lease is held.
+ *
+ *	(if a lease break is pending):
+ *
+ *	%F_RDLCK to indicate an exclusive lease needs to be
+ *		changed to a shared lease (or removed).
+ *
+ *	%F_UNLCK to indicate the lease needs to be removed.
+ *
+ *	XXX: sfr & willy disagree over whether F_INPROGRESS
  *	should be returned to userspace.
  */
 int fcntl_getlease(struct file *filp)
 {
 	struct file_lock *fl;
+	int type = F_UNLCK;
 
-	fl = filp->f_dentry->d_inode->i_flock;
-	if ((fl == NULL) || !IS_LEASE(fl))
-		return F_UNLCK;
-	return fl->fl_type & ~F_INPROGRESS;
-}
-
-/* We already had a lease on this file; just change its type */
-static int lease_modify(struct file_lock **before, int arg, int fd, struct file *filp)
-{
-	struct file_lock *fl = *before;
-	int error = assign_type(fl, arg);
-	if (error < 0)
-		goto out;
-
-	locks_wake_up_blocks(fl);
-
-	if (arg == F_UNLCK) {
-		filp->f_owner.pid = 0;
-		filp->f_owner.uid = 0;
-		filp->f_owner.euid = 0;
-		filp->f_owner.signum = 0;
-		locks_delete_lock(before);
-		fasync_helper(fd, filp, 0, &fl->fl_fasync);
+	lock_kernel();
+	time_out_leases(filp->f_dentry->d_inode);
+	for (fl = filp->f_dentry->d_inode->i_flock; fl && IS_LEASE(fl);
+			fl = fl->fl_next) {
+		if (fl->fl_file == filp) {
+			type = fl->fl_type & ~F_INPROGRESS;
+			break;
 		}
-
-out:
-	return error;
+	}
+	unlock_kernel();
+	return type;
 }
 
 /**
@@ -1201,50 +1243,59 @@ int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
 	if (!S_ISREG(inode->i_mode))
 		return -EINVAL;
 
+	lock_kernel();
+
+	time_out_leases(inode);
+
 	/*
 	 * FIXME: What about F_RDLCK and files open for writing?
 	 */
+	error = -EAGAIN;
 	if ((arg == F_WRLCK)
 	    && ((atomic_read(&dentry->d_count) > 1)
 		|| (atomic_read(&inode->i_count) > 1)))
-		return -EAGAIN;
-
-	before = &inode->i_flock;
-
-	lock_kernel();
+		goto out_unlock;
 
-	while ((fl = *before) != NULL) {
-		if (!IS_LEASE(fl))
-			break;
+	/*
+	 * At this point, we know that if there is an exclusive
+	 * lease on this file, then we hold it on this filp
+	 * (otherwise our open of this file would have blocked).
+	 * And if we are trying to acquire an exclusive lease,
+	 * then the file is not open by anyone (including us)
+	 * except for this filp.
+	 */
+	for (before = &inode->i_flock;
+			((fl = *before) != NULL) && IS_LEASE(fl);
+			before = &fl->fl_next) {
 		if (fl->fl_file == filp)
 			my_before = before;
-		else if (fl->fl_type & F_WRLCK)
+		else if (fl->fl_type == (F_INPROGRESS | F_UNLCK))
+			/*
+			 * Someone is in the process of opening this
+			 * file for writing so we may not take an
+			 * exclusive lease on it.
+			 */
 			wrlease_count++;
 		else
 			rdlease_count++;
-		before = &fl->fl_next;
 	}
 
 	if ((arg == F_RDLCK && (wrlease_count > 0)) ||
-	    (arg == F_WRLCK && ((rdlease_count + wrlease_count) > 0))) {
-		error = -EAGAIN;
+	    (arg == F_WRLCK && ((rdlease_count + wrlease_count) > 0)))
 		goto out_unlock;
-	}
 
 	if (my_before != NULL) {
-		error = lease_modify(my_before, arg, fd, filp);
+		error = lease_modify(my_before, arg);
 		goto out_unlock;
 	}
 
-	if (arg == F_UNLCK) {
 	error = 0;
+	if (arg == F_UNLCK)
 		goto out_unlock;
-	}
 
-	if (!leases_enable) {
 	error = -EINVAL;
+	if (!leases_enable)
 		goto out_unlock;
-	}
 
 	error = lease_alloc(filp, arg, &fl);
 	if (error)
@@ -1616,10 +1667,16 @@ void locks_remove_flock(struct file *filp)
 	before = &inode->i_flock;
 
 	while ((fl = *before) != NULL) {
-		if ((IS_FLOCK(fl) || IS_LEASE(fl)) && (fl->fl_file == filp)) {
+		if (fl->fl_file == filp) {
+			if (IS_FLOCK(fl)) {
 				locks_delete_lock(before);
 				continue;
 			}
+			if (IS_LEASE(fl)) {
+				lease_modify(before, F_UNLCK);
+				continue;
+			}
+ 		}
 		before = &fl->fl_next;
 	}
 	unlock_kernel();
@@ -1673,7 +1730,13 @@ static void lock_get_status(char* out, struct file_lock *fl, int id, char *pfx)
 			out += sprintf(out, "FLOCK  ADVISORY  ");
 		}
 	} else if (IS_LEASE(fl)) {
-		out += sprintf(out, "LEASE  MANDATORY ");
+		out += sprintf(out, "LEASE  ");
+		if (fl->fl_type & F_INPROGRESS)
+			out += sprintf(out, "BREAKING  ");
+		else if (fl->fl_file)
+			out += sprintf(out, "ACTIVE    ");
+		else
+			out += sprintf(out, "BREAKER   ");
 	} else {
 		out += sprintf(out, "UNKNOWN UNKNOWN  ");
 	}
@@ -1684,7 +1747,9 @@ static void lock_get_status(char* out, struct file_lock *fl, int id, char *pfx)
 			       : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
 	} else {
 		out += sprintf(out, "%s ",
-			       (fl->fl_type & F_WRLCK) ? "WRITE" : "READ ");
+			       (fl->fl_type & F_INPROGRESS)
+			       ? (fl->fl_type & F_UNLCK) ? "UNLCK" : "READ "
+			       : (fl->fl_type & F_WRLCK) ? "WRITE" : "READ ");
 	}
 	out += sprintf(out, "%d %s:%ld ",
 		     fl->fl_pid,

include/linux/fs.h

@@ -554,6 +554,7 @@ struct file_lock {
 	void (*fl_remove)(struct file_lock *);	/* lock removal callback */
 
 	struct fasync_struct *	fl_fasync; /* for lease break notifications */
+	unsigned long fl_break_time;	/* for nonblocking lease breaks */
 
 	union {
 		struct nfs_lock_info	nfs_fl;