[PATCH] new tty buffering locking fix

Change locking in the new tty buffering facility from using tty->read_lock,
which is currently ignored by drivers and thus ineffective.  New locking
uses a new tty buffering specific lock enforced centrally in the tty
buffering code.

Two drivers (esp and cyclades) are updated to use the tty buffering
functions instead of accessing tty buffering internals directly.  This is
required for the new locking to work.

Minor checks for NULL buffers added to
tty_prepare_flip_string/tty_prepare_flip_string_flags

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, 13 insertions, 1 deletions

diff --git a/include/linux/kbd_kern.h b/include/linux/kbd_kern.h
index 45f625d7d0b2..3aed37314ab8 100644
--- a/include/linux/kbd_kern.h
+++ b/include/linux/kbd_kern.h
@@ -151,6 +151,11 @@ extern unsigned int keymap_count;
 
 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)
+                t->buf.tail->active = 0;
+        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 3787102e4b12..a7bd3b4558d2 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -57,6 +57,7 @@ struct tty_buffer {
         unsigned char *flag_buf_ptr;
         int used;
         int size;
+        int active;
         /* Data points here */
         unsigned long data[0];
 };
@@ -64,6 +65,7 @@ struct tty_buffer {
 struct tty_bufhead {
         struct work_struct              work;
         struct semaphore pty_sem;
+        spinlock_t lock;
         struct tty_buffer *head;        /* Queue head */
         struct tty_buffer *tail;        /* Active buffer */
         struct tty_buffer *free;        /* Free queue head */
diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h
index be1400e82482..82961eb19888 100644
--- a/include/linux/tty_flip.h
+++ b/include/linux/tty_flip.h
@@ -17,7 +17,7 @@ _INLINE_ int tty_insert_flip_char(struct tty_struct *tty,
                                    unsigned char ch, char flag)
 {
         struct tty_buffer *tb = tty->buf.tail;
-        if (tb && tb->used < tb->size) {
+        if (tb && tb->active && tb->used < tb->size) {
                 tb->flag_buf_ptr[tb->used] = flag;
                 tb->char_buf_ptr[tb->used++] = ch;
                 return 1;
@@ -27,6 +27,11 @@ _INLINE_ int tty_insert_flip_char(struct tty_struct *tty,
 
 _INLINE_ void tty_schedule_flip(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);
         schedule_delayed_work(&tty->buf.work, 1);
 }