linux-kernel - RE: [PATCH V3 3/7] Drivers: hv: vmbus: add APIs to send/recv hvsock packet and get the r/w-ability

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Date:	Thu, 23 Jul 2015 11:05:48 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
CC:	"pebolle@...cali.nl" <pebolle@...cali.nl>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>,
	"stefanha@...hat.com" <stefanha@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"apw@...onical.com" <apw@...onical.com>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: RE: [PATCH V3 3/7] Drivers: hv: vmbus: add APIs to send/recv hvsock
 packet and get the r/w-ability

> From: Dan Carpenter
> Sent: Thursday, July 23, 2015 18:25
> On Thu, Jul 23, 2015 at 01:10:57PM +0300, Dan Carpenter wrote:
> > In this specific case, writing it as "if (ret != 0)" caused the bug.  If
> > we had written it as "if (ret) return ret;" then there are no zeroes so
> > wouldn't have been any temptation to return the zero instead of the ret.
> 
> I did a search to see if returning the zero instead of the ret was a
> common mistake and it seems like it might be.  I did:
> 
> grep 'if (ret != 0)' drivers/   -r -A1 -n | grep "return 0;" | perl -ne 's/.c-(\d+)-/.c:$1/;
> print'
> 
> drivers/gpu/drm/nouveau/nouveau_display.c:111                   return 0;
> drivers/regulator/wm8400-regulator.c:47         return 0;
> drivers/platform/x86/dell-laptop.c:859          return 0;
> drivers/media/dvb-frontends/dibx000_common.c:213                                return 0;
> drivers/media/dvb-frontends/dibx000_common.c:217                                return 0;
> drivers/media/dvb-frontends/dibx000_common.c:235                                return 0;
> drivers/media/dvb-frontends/dibx000_common.c:239                                return 0;
> drivers/hv/channel.c:898                return 0;
> drivers/hv/channel.c:944                return 0;
> 
> A bunch of those look suspicious but I don't know the subsystems well
> enough to be sure.  Can you check the last two?
> 
> dan carpenter

Thanks, Dan!

After I checked the code, I think there is no issue for the last two:
in the case of "if (ret != 0) return 0;",  the output parameter buffer_actual_len is
zero and it is explicitly checked by the callers.
This may seem not natural and I think we can improve it in future.

BTW, at the end of vmbus_recvpacket(), the "return 0;" should be "return ret;", but
since the output parameter buffer_actual_len is checked by the callers, I think it's
OK for now.

Thanks,
-- Dexuan
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