2018-01-27 10:03:52

by Jia-Ju Bai

Subject: [PATCH] bluetooth: hci_ll: Replace mdelay with msleep in download_firmware

download_firmware() is never called from atomic context.

It is only called by ll_setup() that is called only via function pointer
"->setup" used in hci_uart_setup() in drivers/bluetooth/hci_serdev.c and
drivers/bluetooth/hci_ldisc.c. hci_uart_setup() is called only
via function pointer "->setup" used in hci_dev_do_open()
in net/bluetooth/hci_core.c.
All of the above functions do not enter atomic context.

Besides, ll_setup() calls msleep() and hci_dev_do_open calls mutex_lock().
So it indicates that all the above functions call functions that can sleep.

Despite never getting called from atomic context, download_firmware()
calls mdelay() for busy wait.
That is not necessary and can be replaced with msleep to avoid busy wait.

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
drivers/bluetooth/hci_ll.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/bluetooth/hci_ll.c b/drivers/bluetooth/hci_ll.c
index e2c078d..f804adc 100644
--- a/drivers/bluetooth/hci_ll.c
+++ b/drivers/bluetooth/hci_ll.c
@@ -644,7 +644,7 @@ static int download_firmware(struct ll_device *lldev)
break;
case ACTION_DELAY: /* sleep */
bt_dev_info(lldev->hu.hdev, "sleep command in scr");
- mdelay(((struct bts_action_delay *)action_ptr)->msec);
+ msleep(((struct bts_action_delay *)action_ptr)->msec);
break;
}
len -= (sizeof(struct bts_action) +
--
1.7.9.5

2018-02-07 08:55:46

by Marcel Holtmann

Subject: Re: [PATCH] bluetooth: hci_ll: Replace mdelay with msleep in download_firmware

Hi Jia-Ju,

> download_firmware() is never called from atomic context.
>
> It is only called by ll_setup() that is called only via function pointer
> "->setup" used in hci_uart_setup() in drivers/bluetooth/hci_serdev.c and
> drivers/bluetooth/hci_ldisc.c. hci_uart_setup() is called only
> via function pointer "->setup" used in hci_dev_do_open()
> in net/bluetooth/hci_core.c.
> All of the above functions do not enter atomic context.
>
> Besides, ll_setup() calls msleep() and hci_dev_do_open calls mutex_lock().
> So it indicates that all the above functions call functions that can sleep.
>
> Despite never getting called from atomic context, download_firmware()
> calls mdelay() for busy wait.
> That is not necessary and can be replaced with msleep to avoid busy wait.
>
> This is found by a static analysis tool named DCNS written by myself.
>
> Signed-off-by: Jia-Ju Bai <[email protected]>
> ---
> drivers/bluetooth/hci_ll.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

patch has been applied to bluetooth-next tree.

Regards

Marcel