The following commit has been merged in the linux branch: commit 45242006e19c6f99945554e4d7d5680caf6ed9ad Author: Linus Torvalds torvalds@linux-foundation.org Date: Wed Oct 14 08:59:49 2009 -0700

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 --- 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);