Make flush_to_ldisc properly handle parallel calls

diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
index 3108991..0296612 100644 (file)
--- a/drivers/char/tty_buffer.c
+++ b/drivers/char/tty_buffer.c
@@ -402,28 +402,26 @@ static void flush_to_ldisc(struct work_struct *work)
                container_of(work, struct tty_struct, buf.work.work);
        unsigned long   flags;
        struct tty_ldisc *disc;
-       struct tty_buffer *tbuf, *head;
-       char *char_buf;
-       unsigned char *flag_buf;
 
        disc = tty_ldisc_ref(tty);
        if (disc == NULL)       /*  !TTY_LDISC */
                return;
 
        spin_lock_irqsave(&tty->buf.lock, flags);
-       /* So we know a flush is running */
-       set_bit(TTY_FLUSHING, &tty->flags);
-       head = tty->buf.head;
-       if (head != NULL) {
-               tty->buf.head = NULL;
-               for (;;) {
-                       int count = head->commit - head->read;
+
+       if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
+               struct tty_buffer *head;
+               while ((head = tty->buf.head) != NULL) {
+                       int count;
+                       char *char_buf;
+                       unsigned char *flag_buf;
+
+                       count = head->commit - head->read;
                        if (!count) {
                                if (head->next == NULL)
                                        break;
-                               tbuf = head;
-                               head = head->next;
-                               tty_buffer_free(tty, tbuf);
+                               tty->buf.head = head->next;
+                               tty_buffer_free(tty, head);
                                continue;
                        }
                        /* Ldisc or user is trying to flush the buffers
@@ -445,9 +443,9 @@ static void flush_to_ldisc(struct work_struct *work)
                                                        flag_buf, count);
                        spin_lock_irqsave(&tty->buf.lock, flags);
                }
-               /* Restore the queue head */
-               tty->buf.head = head;
+               clear_bit(TTY_FLUSHING, &tty->flags);
        }
+
        /* We may have a deferred request to flush the input buffer,
           if so pull the chain under the lock and empty the queue */
        if (test_bit(TTY_FLUSHPENDING, &tty->flags)) {
@@ -455,7 +453,6 @@ static void flush_to_ldisc(struct work_struct *work)
                clear_bit(TTY_FLUSHPENDING, &tty->flags);
                wake_up(&tty->read_wait);
        }
-       clear_bit(TTY_FLUSHING, &tty->flags);
        spin_unlock_irqrestore(&tty->buf.lock, flags);
 
        tty_ldisc_deref(disc);