staging: dgnc: Fix a sleep-in-atomic-context bug in cls_assert_modem_signals()

The driver may sleep with holding a spinlock.
The function call path (from bottom to top) in Linux-4.17 is:

[FUNC] usleep_range
drivers/staging/dgnc/dgnc_cls.c, 391:
	usleep_range in cls_assert_modem_signals
drivers/staging/dgnc/dgnc_cls.c, 449:
	cls_assert_modem_signals in cls_copy_data_from_queue_to_uart
drivers/staging/dgnc/dgnc_cls.c, 406:
	_raw_spin_lock_irqsave in cls_copy_data_from_queue_to_uart

To fix this bug, usleep_range() is replaced with udelay().

This bug is found by my static analysis tool DSAC.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/dgnc/dgnc_cls.c b/drivers/staging/dgnc/dgnc_cls.c
index 7e6cbfe..a1e98ee 100644 (file)
--- a/drivers/staging/dgnc/dgnc_cls.c
+++ b/drivers/staging/dgnc/dgnc_cls.c
@@ -388,7 +388,7 @@ static void cls_assert_modem_signals(struct channel_t *ch)
        writeb(out, &ch->ch_cls_uart->mcr);
 
        /* Give time for the UART to actually drop the signals */
-       usleep_range(10, 20);
+       udelay(20);
 }
 
 static void cls_copy_data_from_queue_to_uart(struct channel_t *ch)