tty: replace BKL with a new tty_lock

As a preparation for replacing the big kernel lock
in the TTY layer, wrap all the callers in new
macros tty_lock, tty_lock_nested and tty_unlock.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 2df60e4ff40..6ead6b60c74 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -13,6 +13,7 @@
 #include <linux/tty_driver.h>
 #include <linux/tty_ldisc.h>
 #include <linux/mutex.h>
+#include <linux/smp_lock.h>
 
 #include <asm/system.h>
 
@@ -576,5 +577,35 @@ extern int vt_ioctl(struct tty_struct *tty, struct file *file,
 extern long vt_compat_ioctl(struct tty_struct *tty, struct file * file,
 		     unsigned int cmd, unsigned long arg);
 
+/* functions for preparation of BKL removal */
+
+/*
+ * tty_lock_nested get the tty_lock while potentially holding it
+ *
+ * The Big TTY Mutex is a recursive lock, meaning you can take it
+ * from a thread that is already holding it.
+ * This is bad for a number of reasons, so tty_lock_nested should
+ * really be used as rarely as possible. If a code location can
+ * be shown to never get called with this held already, it should
+ * use tty_lock() instead.
+ */
+static inline void __lockfunc tty_lock_nested(void) __acquires(kernel_lock)
+{
+	lock_kernel();
+}
+static inline void tty_lock(void) __acquires(kernel_lock)
+{
+#ifdef CONFIG_LOCK_KERNEL
+	/* kernel_locked is 1 for !CONFIG_LOCK_KERNEL */
+	WARN_ON(kernel_locked());
+#endif
+	lock_kernel();
+}
+static inline void tty_unlock(void) __releases(kernel_lock)
+{
+	unlock_kernel();
+}
+#define tty_locked()		(kernel_locked())
+
 #endif /* __KERNEL__ */
 #endif