[PATCH] tty buffering stall fix

Prevent stalled processing of received data when a driver allocates tty
buffer space but does not immediately follow the allocation with more data
and a call to schedule receive tty processing.  (example: hvc_console) This
bug was introduced by the first locking patch for the new tty buffering.

Signed-off-by: Paul Fulghum <paulkf@microgate.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 8 insertions, 2 deletions

diff --git a/include/linux/kbd_kern.h b/include/linux/kbd_kern.h
index 3aed37314ab8..e87c32a5c86a 100644
--- a/include/linux/kbd_kern.h
+++ b/include/linux/kbd_kern.h
@@ -153,8 +153,10 @@ static inline void con_schedule_flip(struct tty_struct *t)
 {
         unsigned long flags;
         spin_lock_irqsave(&t->buf.lock, flags);
-        if (t->buf.tail != NULL)
+        if (t->buf.tail != NULL) {
                 t->buf.tail->active = 0;
+                t->buf.tail->commit = t->buf.tail->used;
+        }
         spin_unlock_irqrestore(&t->buf.lock, flags);
         schedule_work(&t->buf.work);
 }
diff --git a/include/linux/tty.h b/include/linux/tty.h
index a7bd3b4558d2..f45cd74e6f24 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -58,6 +58,8 @@ struct tty_buffer {
         int used;
         int size;
         int active;
+        int commit;
+        int read;
         /* Data points here */
         unsigned long data[0];
 };
diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h
index 82961eb19888..222faf97d5f9 100644
--- a/include/linux/tty_flip.h
+++ b/include/linux/tty_flip.h
@@ -29,8 +29,10 @@ _INLINE_ void tty_schedule_flip(struct tty_struct *tty)
 {
         unsigned long flags;
         spin_lock_irqsave(&tty->buf.lock, flags);
-        if (tty->buf.tail != NULL)
+        if (tty->buf.tail != NULL) {
                 tty->buf.tail->active = 0;
+                tty->buf.tail->commit = tty->buf.tail->used;
+        }
         spin_unlock_irqrestore(&tty->buf.lock, flags);
         schedule_delayed_work(&tty->buf.work, 1);
 }