linux-kernel - RE: [PATCH 1/2] staging: hv: Fix race condition in hv

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Date:	Wed, 19 May 2010 22:12:51 +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 1/2] staging: hv: Fix race condition in hv_utils module
 initialization.

> > Actually, we already assign a default callback function,
> chn_cb_negotiate(),
> > when the channels are opened in vmbus module. It's a real function
> and can
> > handle common negotiation messages.
> 
> Then why don't you use it here?

When vmbus is loaded and channel is offered from HyperV host, the default
callback function, chn_cb_negotiate(), is assigned to the function ptr, and
used to do basic responses of negotiation messages. 

After hv_utils modules is loaded the callback function ptr is overridden by 
a specialized function in hv_utils module, and handles each feature (shutdown, 
timesync, etc.) differently.

> I still think there's a real problem somewhere else in the architecture
> if such a sleep is necessary...
> 
> Is the issue that the modprobe of the hv_vmbus can return before the
> bus
> is really all set up and ready to go?  If so, just fix that, then you
> will not need any "sleep" calls anywhere, right?

After vmbus is loaded, the channel offering will come from the host, then
it initializes the channel. The channel offering can happen a little later
after vmbus_init() is done and modprobe returns. So I think we should let
vmbus_init function wait(sleep) until all channel offerings are received before
returning. This will ensure all channels are ready before modprobe returns.

Thanks,

- Haiyang
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