linux-kernel - RE: [PATCH 1/1] staging: hv: Fix race condition on IC channel initialization

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Date:	Fri, 21 May 2010 22:07:17 +0000
From:	Haiyang Zhang <haiyangz@...rosoft.com>
To:	Greg KH <gregkh@...e.de>
CC:	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'devel@...verdev.osuosl.org'" <devel@...verdev.osuosl.org>,
	"'virtualization@...ts.osdl.org'" <virtualization@...ts.osdl.org>,
	"Hank Janssen" <hjanssen@...rosoft.com>
Subject: RE: [PATCH 1/1] staging: hv: Fix race condition on IC channel
 initialization

> From: Greg KH [mailto:gregkh@...e.de]
> > +/* 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);
> 
> 
> this turns into a simple function call, again, never needing to know
> about message types or any other mess.

This looks good. I will add the hv_vmbus_ready() function. It doesn't even 
have to be exported symbol, because it's only used in vmbus module to ensure 
all channels are ready before vmbus_init() returns. Other modules won't get a 
chance to see uninitialized channels after hv_vmbus is loaded.

Also, I'll cleanup the printk in hv_utils load/unload.

Regarding the atomic variable -- the channel offer processing function is 
triggered by interrupts from host -- should we be concerned about "counter++" 
racing with each other in two interrupts happening around the same time?

Thanks,

- Haiyang

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