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

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Message-ID: <1FB5E1D5CA062146B38059374562DF7266B8C775@TK5EX14MBXC128.redmond.corp.microsoft.com>
Date:	Wed, 26 May 2010 22:23:08 +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 (modified)

> 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().

> > 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?

Thanks,

- Haiyang

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