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

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Message-ID: <1FB5E1D5CA062146B38059374562DF7266B8C0B7@TK5EX14MBXC128.redmond.corp.microsoft.com>
Date:	Tue, 25 May 2010 23:14:48 +0000
From:	Haiyang Zhang <haiyangz@...rosoft.com>
To:	Ky Srinivasan <ksrinivasan@...ell.com>, Greg KH <gregkh@...e.de>
CC:	"'devel@...verdev.osuosl.org'" <devel@...verdev.osuosl.org>,
	"'virtualization@...ts.osdl.org'" <virtualization@...ts.osdl.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/1] staging: hv: Fix race condition on IC channel
	 initialization

> From: Ky Srinivasan [mailto:ksrinivasan@...ell.com]
> You would need to protect the increment, if interrupts are going to
> come in on any cpu and update the counter. While in your current
> implementation interrupts are only delivered on cpu0, it is still
> probably good to deal with the more general case and protect the
> counter.
> 
> On a slightly different note, why don't you make the synchronization
> more explicit than what you currently have: Rather than polling the
> variable in a loop, why don't you put that context to sleep and the
> interrupt context that updates the count would be responsible for
> issuing the wakeup when the conditions are appropriate - when all
> channels are initialized.

Thank you for the suggestion. I will keep the counter atomic to handle 
more general case potentially. To ensure channels are ready before 
vmbus_init() returns, I used an event waiting mechanism instead of 
polling the variable periodically. A modified patch will be submitted 
soon.

Thanks,

- Haiyang

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