[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>

4 files changed, 30 insertions, 10 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 076e07c1da38..a23816d3e9a1 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -268,6 +268,8 @@ static struct tty_buffer *tty_buffer_alloc(size_t size)
         p->size = size;
         p->next = NULL;
         p->active = 0;
+        p->commit = 0;
+        p->read = 0;
         p->char_buf_ptr = (char *)(p->data);
         p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
 /*      printk("Flip create %p\n", p); */
@@ -298,6 +300,8 @@ static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
                         *tbh = t->next;
                         t->next = NULL;
                         t->used = 0;
+                        t->commit = 0;
+                        t->read = 0;
                         /* DEBUG ONLY */
                         memset(t->data, '*', size);
 /*                      printk("Flip recycle %p\n", t); */
@@ -335,6 +339,7 @@ int tty_buffer_request_room(struct tty_struct *tty, size_t size)
                         if (b != NULL) {
                                 b->next = n;
                                 b->active = 0;
+                                b->commit = b->used;
                         } else
                                 tty->buf.head = n;
                         tty->buf.tail = n;
@@ -2752,6 +2757,9 @@ static void flush_to_ldisc(void *private_)
         unsigned long   flags;
         struct tty_ldisc *disc;
         struct tty_buffer *tbuf;
+        int count;
+        char *char_buf;
+        unsigned char *flag_buf;
 
         disc = tty_ldisc_ref(tty);
         if (disc == NULL)       /*  !TTY_LDISC */
@@ -2765,16 +2773,20 @@ static void flush_to_ldisc(void *private_)
                 goto out;
         }
         spin_lock_irqsave(&tty->buf.lock, flags);
-        while((tbuf = tty->buf.head) != NULL && !tbuf->active) {
+        while((tbuf = tty->buf.head) != NULL) {
+                while ((count = tbuf->commit - tbuf->read) != 0) {
+                        char_buf = tbuf->char_buf_ptr + tbuf->read;
+                        flag_buf = tbuf->flag_buf_ptr + tbuf->read;
+                        tbuf->read += count;
+                        spin_unlock_irqrestore(&tty->buf.lock, flags);
+                        disc->receive_buf(tty, char_buf, flag_buf, count);
+                        spin_lock_irqsave(&tty->buf.lock, flags);
+                }
+                if (tbuf->active)
+                        break;
                 tty->buf.head = tbuf->next;
                 if (tty->buf.head == NULL)
                         tty->buf.tail = NULL;
-                spin_unlock_irqrestore(&tty->buf.lock, flags);
-                /* printk("Process buffer %p for %d\n", tbuf, tbuf->used); */
-                disc->receive_buf(tty, tbuf->char_buf_ptr,
-                                       tbuf->flag_buf_ptr,
-                                       tbuf->used);
-                spin_lock_irqsave(&tty->buf.lock, flags);
                 tty_buffer_free(tty, tbuf);
         }
         spin_unlock_irqrestore(&tty->buf.lock, flags);
@@ -2871,8 +2883,10 @@ void tty_flip_buffer_push(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);
 
         if (tty->low_latency)
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);
 }