linux-kernel - Re: [PATCH] PCI: Mark expected switch fall-throughs

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Date:   Wed, 20 Mar 2019 14:24:54 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] PCI: Mark expected switch fall-throughs

On Wed, Mar 20, 2019 at 01:27:15PM -0500, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch
> cases where we are expecting to fall through.

Does this fix all the remaining cases in drivers/pci?  I'd like to fix
them all at once.

What's the best way to watch for new warnings being added?  I fiddled
with "make W=2" etc but it didn't seem useful.  Does the 0-day robot
warn when -Wimplicit-fallthrough warnings are added?

Bjorn

> This patch fixes the following warnings:
> 
> drivers/pci/proc.c: In function ‘proc_bus_pci_ioctl’:
> drivers/pci/proc.c:216:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    if (arch_can_pci_mmap_wc()) {
>       ^
> drivers/pci/proc.c:225:2: note: here
>   default:
>   ^~~~~~~
> 
> drivers/pci/xen-pcifront.c: In function ‘pcifront_backend_changed’:
> drivers/pci/xen-pcifront.c:1105:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
>    if (xdev->state == XenbusStateClosed)
>       ^
> drivers/pci/xen-pcifront.c:1108:2: note: here
>   case XenbusStateClosing:
>   ^~~~
> 
> Notice that, in this particular case, the /* fall through */
> comment is placed at the very bottom of the case statement,
> which is what GCC is expecting to find.
> 
> Warning level 3 was used: -Wimplicit-fallthrough=3
> 
> This patch is part of the ongoing efforts to enable
> -Wimplicit-fallthrough.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/pci/proc.c         | 1 +
>  drivers/pci/xen-pcifront.c | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
> index 6fa1627ce08d..445b51db75b0 100644
> --- a/drivers/pci/proc.c
> +++ b/drivers/pci/proc.c
> @@ -222,6 +222,7 @@ static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
>  		}
>  		/* If arch decided it can't, fall through... */
>  #endif /* HAVE_PCI_MMAP */
> +		/* fall through */
>  	default:
>  		ret = -EINVAL;
>  		break;
> diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
> index eba6e33147a2..14cf0f41ecf0 100644
> --- a/drivers/pci/xen-pcifront.c
> +++ b/drivers/pci/xen-pcifront.c
> @@ -1104,7 +1104,7 @@ static void __ref pcifront_backend_changed(struct xenbus_device *xdev,
>  	case XenbusStateClosed:
>  		if (xdev->state == XenbusStateClosed)
>  			break;
> -		/* Missed the backend's CLOSING state -- fallthrough */
> +		/* fall through - Missed the backend's CLOSING state. */
>  	case XenbusStateClosing:
>  		dev_warn(&xdev->dev, "backend going away!\n");
>  		pcifront_try_disconnect(pdev);
> -- 
> 2.21.0
>