linux-kernel - Re: [PATCH] USB: core: Improve unlocking of a mutex in two functions

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Date:   Sun, 5 Nov 2017 00:25:19 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     USB list <linux-usb@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Eugene Korenevsky <ekorenevsky@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Günter Röck <linux@...ck-us.net>,
        Jaejoong Kim <climbbb.kim@...il.com>,
        Johan Hovold <johan@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH] USB: core: Improve unlocking of a mutex in two functions

On Sat, Nov 4, 2017 at 9:12 PM, SF Markus Elfring
<elfring@...rs.sourceforge.net> wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Sat, 4 Nov 2017 21:00:46 +0100
>
> * Add jump targets so that a call of the function "mutex_unlock" is stored
>   only twice in these function implementations.
>
> * Replace five calls by goto statements.
>
> This issue was detected by using the Coccinelle software.
>
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>

NAKed-by: Geert Uytterhoeven <geert@...ux-m68k.org>

> ---
>  drivers/usb/core/hub.c     |  8 ++++----
>  drivers/usb/core/message.c | 18 ++++++++++--------
>  2 files changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 196a0a5540ed..8f3067c2015c 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -5518,8 +5518,7 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
>                 dev_warn(&udev->dev,
>                                 "Busted HC?  Not enough HCD resources for "
>                                 "old configuration.\n");
> -               mutex_unlock(hcd->bandwidth_mutex);
> -               goto re_enumerate;
> +               goto unlock;
>         }
>         ret = usb_control_msg(udev, usb_sndctrlpipe(udev, 0),
>                         USB_REQ_SET_CONFIGURATION, 0,
> @@ -5529,8 +5528,7 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
>                 dev_err(&udev->dev,
>                         "can't restore configuration #%d (error=%d)\n",
>                         udev->actconfig->desc.bConfigurationValue, ret);
> -               mutex_unlock(hcd->bandwidth_mutex);
> -               goto re_enumerate;
> +               goto unlock;
>         }
>         mutex_unlock(hcd->bandwidth_mutex);
>         usb_set_device_state(udev, USB_STATE_CONFIGURED);
> @@ -5583,6 +5581,8 @@ static int usb_reset_and_verify_device(struct usb_device *udev)
>         udev->bos = bos;
>         return 0;
>
> +unlock:
> +       mutex_unlock(hcd->bandwidth_mutex);

This makes it harder for the reader, as the mutex_unlock() is now far
below the block
of code that's protected by the lock.

>  re_enumerate:
>         usb_release_bos_descriptor(udev);
>         udev->bos = bos;
> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> index 371a07d874a3..fe8e36cc7def 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -1321,8 +1321,8 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
>          */
>         if (usb_disable_lpm(dev)) {
>                 dev_err(&iface->dev, "%s Failed to disable LPM\n.", __func__);
> -               mutex_unlock(hcd->bandwidth_mutex);
> -               return -ENOMEM;
> +               ret = -ENOMEM;
> +               goto unlock;
>         }
>         /* Changing alt-setting also frees any allocated streams */
>         for (i = 0; i < iface->cur_altsetting->desc.bNumEndpoints; i++)
> @@ -1332,9 +1332,7 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
>         if (ret < 0) {
>                 dev_info(&dev->dev, "Not enough bandwidth for altsetting %d\n",
>                                 alternate);
> -               usb_enable_lpm(dev);
> -               mutex_unlock(hcd->bandwidth_mutex);
> -               return ret;
> +               goto enable_lpm;
>         }
>
>         if (dev->quirks & USB_QUIRK_NO_SET_INTF)
> @@ -1355,9 +1353,7 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
>         } else if (ret < 0) {
>                 /* Re-instate the old alt setting */
>                 usb_hcd_alloc_bandwidth(dev, NULL, alt, iface->cur_altsetting);
> -               usb_enable_lpm(dev);
> -               mutex_unlock(hcd->bandwidth_mutex);
> -               return ret;
> +               goto enable_lpm;
>         }
>         mutex_unlock(hcd->bandwidth_mutex);
>
> @@ -1413,6 +1409,12 @@ int usb_set_interface(struct usb_device *dev, int interface, int alternate)
>                 create_intf_ep_devs(iface);
>         }
>         return 0;
> +
> +enable_lpm:
> +       usb_enable_lpm(dev);
> +unlock:
> +       mutex_unlock(hcd->bandwidth_mutex);

Likewise.

> +       return ret;
>  }
>  EXPORT_SYMBOL_GPL(usb_set_interface);

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds