[PATCH 2/6] leases: fix write-open/read-lease race

[J. Bruce Fields]

In setlease, we use i_writecount to decide whether we can give out a
read lease.

In open, we break leases before incrementing i_writecount.

There is therefore a window between the break lease and the i_writecount
increment when setlease could add a new read lease.

This would leave us with a simultaneous write open and read lease, which
shouldn't happen.

Signed-off-by: J. Bruce Fields <bfields at redhat.com>
---
 fs/namei.c |    5 +----
 fs/open.c  |    4 ++++
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 2826db3..6ff59e5 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2044,10 +2044,7 @@ static int may_open(struct path *path, int acc_mode, int flag)
 	if (flag & O_NOATIME && !inode_owner_or_capable(inode))
 		return -EPERM;
 
-	/*
-	 * Ensure there are no outstanding leases on the file.
-	 */
-	return break_lease(inode, flag);
+	return 0;
 }
 
 static int handle_truncate(struct file *filp)
diff --git a/fs/open.c b/fs/open.c
index f711921..22c41b5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -685,6 +685,10 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
 	if (error)
 		goto cleanup_all;
 
+	error = break_lease(inode, f->f_flags);
+	if (error)
+		goto cleanup_all;
+
 	if (!open && f->f_op)
 		open = f->f_op->open;
 	if (open) {
-- 
1.7.4.1