Re: [Xen-devel] [PATCH] PCI: Mark expected switch fall-throughs

From: "Jan Beulich" <JBeulich@suse.com>
To: "Gustavo A.R.Silva" <gustavo@embeddedor.com>
Cc: <keescook@chromium.org>, "Bjorn Helgaas" <bhelgaas@google.com>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"xen-devel" <xen-devel@lists.xenproject.org>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"Juergen Gross" <jgross@suse.com>, <linux-kernel@vger.kernel.org>,
	<linux-pci@vger.kernel.org>
Subject: Re: [Xen-devel] [PATCH] PCI: Mark expected switch fall-throughs
Date: Mon, 25 Mar 2019 07:25:09 -0600	[thread overview]
Message-ID: <5C98D6B502000078002219FB@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <20190320182715.GA9406@embeddedor>

>>> On 20.03.19 at 19:27, <gustavo@embeddedor.com> wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch
> cases where we are expecting to fall through.
> 
> 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.

None of the above explains why ...

> --- 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. */

... the original comment here wasn't good enough.

Jan