[PATCH v2 6/6] tty: Make tty_files_lock per-tty

[Peter Hurley]

Access to tty->tty_files list is always per-tty, never for all ttys
simultaneously. Replace global tty_files_lock spinlock with per-tty
->files_lock. Initialize when the ->tty_files list is inited, in
alloc_tty_struct().

Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
 drivers/tty/tty_io.c     | 25 ++++++++++++-------------
 include/linux/tty.h      |  2 +-
 security/selinux/hooks.c |  4 ++--
 3 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index b89c0a5..48281a5 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -138,9 +138,6 @@ LIST_HEAD(tty_drivers);			/* linked list of tty drivers */
 /* Mutex to protect creating and releasing a tty */
 DEFINE_MUTEX(tty_mutex);
 
-/* Spinlock to protect the tty->tty_files list */
-DEFINE_SPINLOCK(tty_files_lock);
-
 static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
 static ssize_t tty_write(struct file *, const char __user *, size_t, loff_t *);
 ssize_t redirected_tty_write(struct file *, const char __user *,
@@ -202,9 +199,9 @@ void tty_add_file(struct tty_struct *tty, struct file *file)
 	priv->tty = tty;
 	priv->file = file;
 
-	spin_lock(&tty_files_lock);
+	spin_lock(&tty->files_lock);
 	list_add(&priv->list, &tty->tty_files);
-	spin_unlock(&tty_files_lock);
+	spin_unlock(&tty->files_lock);
 }
 
 /**
@@ -225,10 +222,11 @@ void tty_free_file(struct file *file)
 static void tty_del_file(struct file *file)
 {
 	struct tty_file_private *priv = file->private_data;
+	struct tty_struct *tty = priv->tty;
 
-	spin_lock(&tty_files_lock);
+	spin_lock(&tty->files_lock);
 	list_del(&priv->list);
-	spin_unlock(&tty_files_lock);
+	spin_unlock(&tty->files_lock);
 	tty_free_file(file);
 }
 
@@ -286,11 +284,11 @@ static int check_tty_count(struct tty_struct *tty, const char *routine)
 	struct list_head *p;
 	int count = 0;
 
-	spin_lock(&tty_files_lock);
+	spin_lock(&tty->files_lock);
 	list_for_each(p, &tty->tty_files) {
 		count++;
 	}
-	spin_unlock(&tty_files_lock);
+	spin_unlock(&tty->files_lock);
 	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
 	    tty->driver->subtype == PTY_TYPE_SLAVE &&
 	    tty->link && tty->link->count)
@@ -713,7 +711,7 @@ static void __tty_hangup(struct tty_struct *tty, int exit_session)
 	   workqueue with the lock held */
 	check_tty_count(tty, "tty_hangup");
 
-	spin_lock(&tty_files_lock);
+	spin_lock(&tty->files_lock);
 	/* This breaks for file handles being sent over AF_UNIX sockets ? */
 	list_for_each_entry(priv, &tty->tty_files, list) {
 		filp = priv->file;
@@ -725,7 +723,7 @@ static void __tty_hangup(struct tty_struct *tty, int exit_session)
 		__tty_fasync(-1, filp, 0);	/* can't block */
 		filp->f_op = &hung_up_tty_fops;
 	}
-	spin_unlock(&tty_files_lock);
+	spin_unlock(&tty->files_lock);
 
 	refs = tty_signal_session_leader(tty, exit_session);
 	/* Account for the p->signal references we killed */
@@ -1637,9 +1635,9 @@ static void release_one_tty(struct work_struct *work)
 	tty_driver_kref_put(driver);
 	module_put(owner);
 
-	spin_lock(&tty_files_lock);
+	spin_lock(&tty->files_lock);
 	list_del_init(&tty->tty_files);
-	spin_unlock(&tty_files_lock);
+	spin_unlock(&tty->files_lock);
 
 	put_pid(tty->pgrp);
 	put_pid(tty->session);
@@ -3176,6 +3174,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
 	mutex_init(&tty->atomic_write_lock);
 	spin_lock_init(&tty->ctrl_lock);
 	spin_lock_init(&tty->flow_lock);
+	spin_lock_init(&tty->files_lock);
 	INIT_LIST_HEAD(&tty->tty_files);
 	INIT_WORK(&tty->SAK_work, do_SAK_work);
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 8ed795d..dea7d54 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -302,6 +302,7 @@ struct tty_struct {
 	struct work_struct hangup_work;
 	void *disc_data;
 	void *driver_data;
+	spinlock_t files_lock;		/* protects tty_files list */
 	struct list_head tty_files;
 
 #define N_TTY_BUF_SIZE 4096
@@ -508,7 +509,6 @@ extern int tty_standard_install(struct tty_driver *driver,
 		struct tty_struct *tty);
 
 extern struct mutex tty_mutex;
-extern spinlock_t tty_files_lock;
 
 #define tty_is_writelocked(tty)  (mutex_is_locked(&tty->atomic_write_lock))
 
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index d0cfaa9..ae6dbc75 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2352,7 +2352,7 @@ static inline void flush_unauthorized_files(const struct cred *cred,
 
 	tty = get_current_tty();
 	if (tty) {
-		spin_lock(&tty_files_lock);
+		spin_lock(&tty->files_lock);
 		if (!list_empty(&tty->tty_files)) {
 			struct tty_file_private *file_priv;
 
@@ -2367,7 +2367,7 @@ static inline void flush_unauthorized_files(const struct cred *cred,
 			if (file_path_has_perm(cred, file, FILE__READ | FILE__WRITE))
 				drop_tty = 1;
 		}
-		spin_unlock(&tty_files_lock);
+		spin_unlock(&tty->files_lock);
 		tty_kref_put(tty);
 	}
 	/* Reset controlling tty. */
-- 
2.7.0