[PATCH v1 10/38] locks: create a new notifier chain for lease attempts

[Jeff Layton <jlayton@poochiereds.net>]

With the new file caching infrastructure in nfsd, we can end up holding
files open for an indefinite period of time, even when they are still
idle. This may prevent the kernel from handing out leases on the file,
which is something we don't want to block.

Fix this by running a SRCU notifier call chain whenever any lease
attempt is made. nfsd can then purge the nfsd_file cache of any entries
associated with that inode, and use the fput_global infrastructure to
make sure the final __fput is done.

Since SRCU is only conditionally compiled in, we must only define the
new chain if it's enabled, and users of the chain must ensure that
SRCU is enabled.

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
---
 fs/locks.c         | 37 +++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  1 +
 2 files changed, 38 insertions(+)

diff --git a/fs/locks.c b/fs/locks.c
index 86c94674ab22..e463d585f77d 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1786,6 +1786,40 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp,
 }
 EXPORT_SYMBOL(generic_setlease);
 
+#if IS_ENABLED(CONFIG_SRCU)
+/*
+ * Kernel subsystems can register to be notified on any attempt to set
+ * a new lease with the lease_notifier_chain. This is used by (e.g.) nfsd
+ * to close files that it may have cached when there is an attempt to set a
+ * conflicting lease.
+ */
+struct srcu_notifier_head lease_notifier_chain;
+EXPORT_SYMBOL_GPL(lease_notifier_chain);
+
+static inline void
+lease_notifier_chain_init(void)
+{
+	srcu_init_notifier_head(&lease_notifier_chain);
+}
+
+static inline void
+setlease_notifier(long arg, struct file_lock *lease)
+{
+	if (arg != F_UNLCK)
+		srcu_notifier_call_chain(&lease_notifier_chain, arg, lease);
+}
+#else /* !IS_ENABLED(CONFIG_SRCU) */
+static inline void
+lease_notifier_chain_init(void)
+{
+}
+
+static inline void
+setlease_notifier(long arg, struct file_lock *lease)
+{
+}
+#endif /* IS_ENABLED(CONFIG_SRCU) */
+
 /**
  * vfs_setlease        -       sets a lease on an open file
  * @filp:	file pointer
@@ -1806,6 +1840,8 @@ EXPORT_SYMBOL(generic_setlease);
 int
 vfs_setlease(struct file *filp, long arg, struct file_lock **lease, void **priv)
 {
+	if (lease)
+		setlease_notifier(arg, *lease);
 	if (filp->f_op->setlease)
 		return filp->f_op->setlease(filp, arg, lease, priv);
 	else
@@ -2726,6 +2762,7 @@ static int __init filelock_init(void)
 	for_each_possible_cpu(i)
 		INIT_HLIST_HEAD(per_cpu_ptr(&file_lock_list, i));
 
+	lease_notifier_chain_init();
 	return 0;
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cbf08d5c246e..0492ff432f01 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1042,6 +1042,7 @@ extern int fcntl_setlease(unsigned int fd, struct file *filp, long arg);
 extern int fcntl_getlease(struct file *filp);
 
 /* fs/locks.c */
+extern struct srcu_notifier_head	lease_notifier_chain;
 void locks_free_lock_context(struct file_lock_context *ctx);
 void locks_free_lock(struct file_lock *fl);
 extern void locks_init_lock(struct file_lock *);
-- 
2.4.3