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Message-Id: <4BF79F9402000030000859D7@sinclair.provo.novell.com>
Date: Sat, 22 May 2010 09:10:44 -0600
From: "Ky Srinivasan" <ksrinivasan@...ell.com>
To: "Greg KH" <gregkh@...e.de>
Cc: "'devel@...verdev.osuosl.org'" <devel@...verdev.osuosl.org>,
"'virtualization@...ts.osdl.org'" <virtualization@...ts.osdl.org>,
"Haiyang Zhang" <haiyangz@...rosoft.com>,
"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] staging: hv: Fix race condition on IC channel
initialization
>>> On 5/21/2010 at 4:55 PM, in message <20100521205527.GB9594@...e.de>, Greg KH
<gregkh@...e.de> wrote:
> On Fri, May 21, 2010 at 02:21:46PM -0600, Ky Srinivasan wrote:
>>
>>
>> >>> On 5/21/2010 at 4:12 PM, in message <20100521201228.GA6712@...e.de>, Greg KH
>> <gregkh@...e.de> wrote:
>> > On Fri, May 21, 2010 at 07:58:26PM +0000, Haiyang Zhang wrote:
>> >> From: Haiyang Zhang <haiyangz@...rosoft.com>
>> >>
>> >> Subject: staging: hv: Fix race condition on IC channel initialization
>> >> There is a possible race condition when hv_utils starts to load immediately
>> >> after hv_vmbus is loading - null pointer error could happen.
>> >> This patch added an atomic counter to ensure all channels are ready before
>> >> vmbus_init() returns. So another module won't have any uninitialized
>> > channel.
>> >
>> > Better, but not quite ready...
>> >
>> >> +/* Counter of IC channels initialized */
>> >> +atomic_t hv_utils_initcnt = ATOMIC_INIT(0);
>> >
>> > This doesn't need to be an atomic variable, does it really?
>> >
>> > Why not have a simple bool variable "vmbus_initialized" or something.
>> > It starts out as false, and then turns true when you are up and ready.
>> > Then provide a function that tests it:
>> > bool hv_vmbus_ready(void)
>> > {
>> > return vmbus_initialized
>> > }
>> > EXPORT_SYMBOL_GPL(hv_vmbus_ready);
>> I agree with Greg; I would go a step further and deal with this issue
>> as part of loading the bus driver. After all, we already have
>> dependencies established for various LIC drivers on the bus driver.
>> The fact that even after the bus driver is loaded we cannot reliably
>> load other drivers implies that there is an additional dependency that
>> is not currently being handled. Why can't we ensure that the bus
>> driver is fully initialized before we are done with loading the bus
>> driver.
>
> Um, I think that is what this patch fixes :)
>
> It just doesn't do it in a way that I think is very good...
Ok, my mistake. When I saw hv_vmbus_ready function being exported, I was under the impression each of the drivers that depend on the bus driver to check if the bus driver was properly initialized.
Regards,
K. Y
>
> thanks,
>
> greg k-h
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