1 files changed, 50 insertions, 27 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index eb8b5be4e24..076e07c1da3 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -253,6 +253,7 @@ static void tty_buffer_free_all(struct tty_struct *tty)
 
 static void tty_buffer_init(struct tty_struct *tty)
 {
+        spin_lock_init(&tty->buf.lock);
         tty->buf.head = NULL;
         tty->buf.tail = NULL;
         tty->buf.free = NULL;
@@ -266,6 +267,7 @@ static struct tty_buffer *tty_buffer_alloc(size_t size)
         p->used = 0;
         p->size = size;
         p->next = NULL;
+        p->active = 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); */
@@ -312,25 +314,36 @@ static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
 
 int tty_buffer_request_room(struct tty_struct *tty, size_t size)
 {
-        struct tty_buffer *b = tty->buf.tail, *n;
-        int left = 0;
+        struct tty_buffer *b, *n;
+        int left;
+        unsigned long flags;
+
+        spin_lock_irqsave(&tty->buf.lock, flags);
 
         /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
            remove this conditional if its worth it. This would be invisible
            to the callers */
-        if(b != NULL)
+        if ((b = tty->buf.tail) != NULL) {
                 left = b->size - b->used;
-        if(left >= size)
-                return size;
-        /* This is the slow path - looking for new buffers to use */
-        n = tty_buffer_find(tty, size);
-        if(n == NULL)
-                return left;
-        if(b != NULL)
-                b->next = n;
-        else
-                tty->buf.head = n;
-        tty->buf.tail = n;
+                b->active = 1;
+        } else
+                left = 0;
+
+        if (left < size) {
+                /* This is the slow path - looking for new buffers to use */
+                if ((n = tty_buffer_find(tty, size)) != NULL) {
+                        if (b != NULL) {
+                                b->next = n;
+                                b->active = 0;
+                        } else
+                                tty->buf.head = n;
+                        tty->buf.tail = n;
+                        n->active = 1;
+                } else
+                        size = left;
+        }
+
+        spin_unlock_irqrestore(&tty->buf.lock, flags);
         return size;
 }
 
@@ -396,10 +409,12 @@ EXPORT_SYMBOL_GPL(tty_insert_flip_string_flags);
 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars, size_t size)
 {
         int space = tty_buffer_request_room(tty, size);
-        struct tty_buffer *tb = tty->buf.tail;
-        *chars = tb->char_buf_ptr + tb->used;
-        memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
-        tb->used += space;
+        if (likely(space)) {
+                struct tty_buffer *tb = tty->buf.tail;
+                *chars = tb->char_buf_ptr + tb->used;
+                memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
+                tb->used += space;
+        }
         return space;
 }
 
@@ -416,10 +431,12 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 int tty_prepare_flip_string_flags(struct tty_struct *tty, unsigned char **chars, char **flags, size_t size)
 {
         int space = tty_buffer_request_room(tty, size);
-        struct tty_buffer *tb = tty->buf.tail;
-        *chars = tb->char_buf_ptr + tb->used;
-        *flags = tb->flag_buf_ptr + tb->used;
-        tb->used += space;
+        if (likely(space)) {
+                struct tty_buffer *tb = tty->buf.tail;
+                *chars = tb->char_buf_ptr + tb->used;
+                *flags = tb->flag_buf_ptr + tb->used;
+                tb->used += space;
+        }
         return space;
 }
 
@@ -2747,20 +2764,20 @@ static void flush_to_ldisc(void *private_)
                 schedule_delayed_work(&tty->buf.work, 1);
                 goto out;
         }
-        spin_lock_irqsave(&tty->read_lock, flags);
-        while((tbuf = tty->buf.head) != NULL) {
+        spin_lock_irqsave(&tty->buf.lock, flags);
+        while((tbuf = tty->buf.head) != NULL && !tbuf->active) {
                 tty->buf.head = tbuf->next;
                 if (tty->buf.head == NULL)
                         tty->buf.tail = NULL;
-                spin_unlock_irqrestore(&tty->read_lock, flags);
+                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->read_lock, flags);
+                spin_lock_irqsave(&tty->buf.lock, flags);
                 tty_buffer_free(tty, tbuf);
         }
-        spin_unlock_irqrestore(&tty->read_lock, flags);
+        spin_unlock_irqrestore(&tty->buf.lock, flags);
 out:
         tty_ldisc_deref(disc);
 }
@@ -2852,6 +2869,12 @@ EXPORT_SYMBOL(tty_get_baud_rate);
 
 void tty_flip_buffer_push(struct tty_struct *tty)
 {
+        unsigned long flags;
+        spin_lock_irqsave(&tty->buf.lock, flags);
+        if (tty->buf.tail != NULL)
+                tty->buf.tail->active = 0;
+        spin_unlock_irqrestore(&tty->buf.lock, flags);
+
         if (tty->low_latency)
                 flush_to_ldisc((void *) tty);
         else