linux-kernel - Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

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Message-ID: <20191008124052.GA11245@andrea.guest.corp.microsoft.com>
Date:   Tue, 8 Oct 2019 14:41:24 +0200
From:   Andrea Parri <parri.andrea@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        "K . Y . Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus
 protocol versions

> > @@ -244,21 +234,18 @@ int vmbus_connect(void)
> >  	 * version.
> >  	 */
> >  
> > -	version = VERSION_CURRENT;
> > +	for (i = 0; ; i++) {
> > +		version = vmbus_versions[i];
> > +		if (version == VERSION_INVAL)
> > +			goto cleanup;
> 
> If you use e.g. ARRAY_SIZE() you can get rid of VERSION_INVAL - and make
> this code look more natural.

Thank you for pointing this out, Vitaly.

IIUC, you're suggesting that I do:

	for (i = 0; i < ARRAY_SIZE(vmbus_versions); i++) {
		version = vmbus_versions[i];

		ret = vmbus_negotiate_version(msginfo, version);
		if (ret == -ETIMEDOUT)
			goto cleanup;

		if (vmbus_connection.conn_state == CONNECTED)
			break;
	}

	if (vmbus_connection.conn_state != CONNECTED)
		break;

and that I remove VERSION_INVAL from vmbus_versions, yes?

Looking at the uses of VERSION_INVAL, I find one remaining occurrence
of this macro in vmbus_bus_resume(), which does:

	if (vmbus_proto_version == VERSION_INVAL ||
	    vmbus_proto_version == 0) {
		...
	}

TBH I'm looking at vmbus_bus_resume() and vmbus_bus_suspend() for the
first time and I'm not sure about how to change such check yet... any
suggestions?

Mmh, I see that vmbus_bus_resume() and vmbus_bus_suspend() can access
vmbus_connection.conn_state: can such accesses race with a concurrent
vmbus_connect()?

Thanks,
  Andrea


> >  
> > -	do {
> >  		ret = vmbus_negotiate_version(msginfo, version);
> >  		if (ret == -ETIMEDOUT)
> >  			goto cleanup;
> >  
> >  		if (vmbus_connection.conn_state == CONNECTED)
> >  			break;
> > -
> > -		version = vmbus_get_next_version(version);
> > -	} while (version != VERSION_INVAL);
> > -
> > -	if (version == VERSION_INVAL)
> > -		goto cleanup;
> > +	}
> >  
> >  	vmbus_proto_version = version;
> >  	pr_info("Vmbus version:%d.%d\n",