linux-kernel - Re: [PATCH] drbd_receiver: mark expected switch fall-throughs

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Date:   Thu, 14 Feb 2019 18:29:45 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Jens Axboe <axboe@...nel.dk>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Lars Ellenberg <lars.ellenberg@...bit.com>
Cc:     drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] drbd_receiver: mark expected switch fall-throughs



On 2/12/19 3:36 PM, Jens Axboe wrote:
> On 2/12/19 2:28 PM, Gustavo A. R. Silva wrote:
>> In preparation to enabling -Wimplicit-fallthrough, mark switch
>> cases where we are expecting to fall through.
>>
>> This patch fixes the following warnings:
>>
>> drivers/block/drbd/drbd_receiver.c: In function ‘drbd_asb_recover_0p’:
>> drivers/block/drbd/drbd_receiver.c:3093:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
>>    if (self == 1 && peer == 0) {
>>       ^
>> drivers/block/drbd/drbd_receiver.c:3098:2: note: here
>>   case ASB_DISCARD_OLDER_PRI:
>>   ^~~~
>> drivers/block/drbd/drbd_receiver.c:3120:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
>>    if (after_sb_0p == ASB_DISCARD_ZERO_CHG)
>>       ^
>> drivers/block/drbd/drbd_receiver.c:3123:2: note: here
>>   case ASB_DISCARD_LEAST_CHG:
>>   ^~~~
>>
>> Warning level 3 was used: -Wimplicit-fallthrough=3
>>
>> Notice that in some cases, the code comment is modified in
>> accordance with what GCC is expecting to find.
>>
>> This patch is part of the ongoing efforts to enable
>> -Wimplicit-fallthrough.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>> ---
>>  drivers/block/drbd/drbd_receiver.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
>> index c7ad88d91a09..78bb763a367d 100644
>> --- a/drivers/block/drbd/drbd_receiver.c
>> +++ b/drivers/block/drbd/drbd_receiver.c
>> @@ -3094,7 +3094,7 @@ static int drbd_asb_recover_0p(struct drbd_peer_device *peer_device) __must_hold
>>  			rv =  1;
>>  			break;
>>  		}
>> -		/* Else fall through to one of the other strategies... */
>> +		/* Else fall through - to one of the other strategies... */
>>  	case ASB_DISCARD_OLDER_PRI:
>>  		if (self == 0 && peer == 1) {
>>  			rv = 1;
>> @@ -3119,7 +3119,7 @@ static int drbd_asb_recover_0p(struct drbd_peer_device *peer_device) __must_hold
>>  		}
>>  		if (after_sb_0p == ASB_DISCARD_ZERO_CHG)
>>  			break;
>> -		/* else: fall through */
>> +		/* Else fall through */
> 
> This is getting really silly, as these two hunks both aptly demonstrate. Can
> we please inject some sanity into this fall through witch hunt?
> 

No witch hunt here.  This work has proved to be very valuable. I've fixed years-old
bugs thanks to this effort.

> The last hunk is updating ANOTHER patch that also attempted to silence this
> stuff.
> 

Yeah. Sorry about that.

Previously, I was using level 2: -Wimplicit-fallthrough=2, but this time I'm
using level 3: -Wimplicit-fallthrough=3, which is stricter and maps to -Wextra.

Thanks
--
Gustavo