linux-kernel - Re: [PATCH 1/1] staging: hv: Fix race condition on IC channel initialization (modified)

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Date:	Wed, 26 May 2010 15:30:53 -0700
From:	Greg KH <gregkh@...e.de>
To:	Haiyang Zhang <haiyangz@...rosoft.com>
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 (modified)

On Wed, May 26, 2010 at 10:23:08PM +0000, Haiyang Zhang wrote:
> > From: Greg KH [mailto:gregkh@...e.de]
> > > As discussed previously, I used atomic_t to handle more general case
> > > if vmbus interrupts happen on every cpu.
> > 
> > Ok, but then you should use a lock to protect the variable, not an
> > atomic_t.
> > If you care about this, because some other thread is looking at it,
> > then
> > you really need to protect it with a lock.  Don't rely on a mb() to get
> > it all correct for you (hint, I doubt it will...)
> 
> Actually, since the interrupts only happen on cpu0, this is not a
> concern. How about use a simple int variable here? Also, remove the
> mb().

How about a lock!

What's so scary about a pretty little semaphore?  They are all cute and
cuddley and don't bite anyone.  You should not be afraid to use them,
they are here to do your bidding.

> > > The ic_channel_ready variable is called by VmbusChannelProcessOffer /
> > > osd_WaitEventSet(ic_channel_ready) to wake up vmbus_init(). So it's
> > > not a local variable.
> > 
> > But again, this logic should be within the init call, as it's part of
> > the proper init sequence.  So just put it in that call please.
> 
> The VmbusChannelProcessOffer() is called from interrupt context, and
> initialize the channels, wake up vmbus_init when all channels are
> ready. If using local variable only, how to pass the channel ready
> info to vmbus_init() which is in a different context?

No, I mean move the logic you added here, into the vmbus_init() call.

thanks,

greg k-h
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