Make flush_to_ldisc properly handle parallel calls

1 files changed, 13 insertions, 16 deletions

diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
index 3108991c5c8b..0296612cc7df 100644
--- 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);