[PATCH] fix serial close hang

2.4/2.5 kernels suffer from an infinitely long hang when a serial tty device
is closed, and there are characters waiting to be sent.  The hang occurs in
tty_wait_until_sent.

There is a timeout 'closing_wait' which defines how long to wait for the TX
buffers to empty; the problem is that the serial layer totally ignores it.
It is stored in two structures, 'info' and 'state'.  It is initialised in
the 'state' structure, but used from the 'info' structure.

It turns out that 'hub6' was also missing.

I'm not currently clear what the expected behaviour should be when the
timeout is changed via setserial, and others have the port open - I've
opted to preserve the timeout until all users close the port.  It's
trivial to change this behaviour though.

drivers/char/serial.c

@@ -3095,36 +3095,52 @@ static int get_async_struct(int line, struct async_struct **ret_info)
 
 	sstate = rs_table + line;
 	sstate->count++;
-	if (sstate->info) {
-		*ret_info = sstate->info;
-		return 0;
-	}
+	info = sstate->info;
+
+	/*
+	 * If the async_struct is already allocated, do the fastpath.
+	 */
+	if (info)
+		goto out;
+
 	info = kmalloc(sizeof(struct async_struct), GFP_KERNEL);
 	if (!info) {
 		sstate->count--;
 		return -ENOMEM;
 	}
+
 	memset(info, 0, sizeof(struct async_struct));
 	init_waitqueue_head(&info->open_wait);
 	init_waitqueue_head(&info->close_wait);
 	init_waitqueue_head(&info->delta_msr_wait);
 	info->magic = SERIAL_MAGIC;
 	info->port = sstate->port;
+	info->hub6 = sstate->hub6;
 	info->flags = sstate->flags;
-	info->io_type = sstate->io_type;
-	info->iomem_base = sstate->iomem_base;
-	info->iomem_reg_shift = sstate->iomem_reg_shift;
 	info->xmit_fifo_size = sstate->xmit_fifo_size;
+	info->state = sstate;
 	info->line = line;
+	info->iomem_base = sstate->iomem_base;
+	info->iomem_reg_shift = sstate->iomem_reg_shift;
+	info->io_type = sstate->io_type;
 	info->tqueue.routine = do_softint;
 	info->tqueue.data = info;
-	info->state = sstate;
+
 	if (sstate->info) {
 		kfree(info);
-		*ret_info = sstate->info;
-		return 0;
+		info = sstate->info;
+	} else {
+		sstate->info = info;
+	}
+
+out:
+	/*
+	 * If this is the first open, copy over some timeouts.
+	 */
+	if (sstate->count == 1) {
+		info->closing_wait = sstate->closing_wait;
 	}
-	*ret_info = sstate->info = info;
+	*ret_info = info;
 	return 0;
 }
 

include/linux/serialP.h

@@ -70,7 +70,7 @@ struct async_struct {
 	int			x_char;	/* xon/xoff character */
 	int			close_delay;
 	unsigned short		closing_wait;
-	unsigned short		closing_wait2;
+	unsigned short		closing_wait2; /* obsolete */
 	int			IER; 	/* Interrupt Enable Register */
 	int			MCR; 	/* Modem control register */
 	int			LCR; 	/* Line control register */