[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>

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 076e07c1da38dc441592d8a98d83804d4ff8afea..a23816d3e9a1684794c8e5a8f1cc0cce26fb61d8 100644 (file)
--- 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 3aed37314ab805de8fe3dcfec0a5282d7035cc54..e87c32a5c86a022dde6ccdfdf03a794ebc327627 100644 (file)
--- 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 a7bd3b4558d26efaa3ed8dae0b5bb53f0d184cab..f45cd74e6f243da99e34deac005b53cf9232c188 100644 (file)
--- 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 82961eb1988861a08c6c459d3d095a1535bf52fb..222faf97d5f9cbdabb6f8bced55f62fc3a7617cd 100644 (file)
--- 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);
 }