tty: introduce wait_event_interruptible_tty

Calling wait_event_interruptible implicitly
releases the BKL when it sleeps, but we need
to do this explcitly when we have converted
it to a mutex.

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, 42 insertions, 0 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 6ead6b60c743..955d72ea71c0 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -607,5 +607,47 @@ static inline void tty_unlock(void) __releases(kernel_lock)
 }
 #define tty_locked()            (kernel_locked())
 
+/*
+ * wait_event_interruptible_tty -- wait for a condition with the tty lock held
+ *
+ * The condition we are waiting for might take a long time to
+ * become true, or might depend on another thread taking the
+ * BTM. In either case, we need to drop the BTM to guarantee
+ * forward progress. This is a leftover from the conversion
+ * from the BKL and should eventually get removed as the BTM
+ * falls out of use.
+ *
+ * Do not use in new code.
+ */
+#define wait_event_interruptible_tty(wq, condition)                     \
+({                                                                      \
+        int __ret = 0;                                                  \
+        if (!(condition)) {                                             \
+                __wait_event_interruptible_tty(wq, condition, __ret);   \
+        }                                                               \
+        __ret;                                                          \
+})
+
+#define __wait_event_interruptible_tty(wq, condition, ret)              \
+do {                                                                    \
+        DEFINE_WAIT(__wait);                                            \
+                                                                        \
+        for (;;) {                                                      \
+                prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE);      \
+                if (condition)                                          \
+                        break;                                          \
+                if (!signal_pending(current)) {                         \
+                        tty_unlock();                                   \
+                        schedule();                                     \
+                        tty_lock();                                     \
+                        continue;                                       \
+                }                                                       \
+                ret = -ERESTARTSYS;                                     \
+                break;                                                  \
+        }                                                               \
+        finish_wait(&wq, &__wait);                                      \
+} while (0)
+
+
 #endif /* __KERNEL__ */
 #endif