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

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Message-ID: <f4bd4e6a-db87-8c21-fd22-f71652bdc14d@embeddedor.com>
Date:   Wed, 20 Mar 2019 14:33:27 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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 3/20/19 2:24 PM, Bjorn Helgaas wrote:
> 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.
> 

These are actually the last ones.

> 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?
> 

0-day robot doesn't know about these warnings yet.  But it certainly
will once we finally enable -Wimplicit-fallthrough.

Add this to your Makefile to see the warnings:

KBUILD_CFLAGS  += $(call cc-option,-Wimplicit-fallthrough=3,)

Thanks
--
Gustavo

> 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
>>