linux-kernel - RE: [PATCH 2/3]: Staging: hv: Use native wait primitives

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Message-ID: <FB42D5CCD7B5934EB1827DB5ED9B850E07085CF8@TK5EX14MBXC104.redmond.corp.microsoft.com>
Date:	Tue, 15 Feb 2011 13:35:56 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>
Subject: RE: [PATCH 2/3]: Staging: hv: Use native wait primitives



> -----Original Message-----
> From: Jiri Slaby [mailto:jirislaby@...il.com]
> Sent: Tuesday, February 15, 2011 4:21 AM
> To: KY Srinivasan
> Cc: gregkh@...e.de; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; virtualization@...ts.osdl.org
> Subject: Re: [PATCH 2/3]: Staging: hv: Use native wait primitives
> 
> On 02/11/2011 06:59 PM, K. Y. Srinivasan wrote:
> > In preperation for getting rid of the osd layer; change
> > the code to use native wait interfaces. As part of this,
> > fixed the buggy implementation in the osd_wait_primitive
> > where the condition was cleared potentially after the
> > condition was signalled.
> ...
> > @@ -566,7 +567,11 @@ int vmbus_establish_gpadl(struct vmbus_channel
> *channel, void *kbuffer,
> >
> >  		}
> >  	}
> > -	osd_waitevent_wait(msginfo->waitevent);
> > +	wait_event_timeout(msginfo->waitevent,
> > +				msginfo->wait_condition,
> > +				msecs_to_jiffies(1000));
> > +	BUG_ON(msginfo->wait_condition == 0);
> 
> The added BUG_ONs all over the code look scary. These shouldn't be
> BUG_ONs at all. You should maybe warn and bail out, but not kill the
> whole machine.

This is Linux code running as a guest on a Windows host; and so the guest cannot
tolerate a failure of the host. In the cases where I have chosen to BUG_ON, there 
is no reasonable recovery possible when the host is non-functional (as determined 
by a non-responsive host). 

> 
> And looking at the code, more appropriate would be completion instead of
> wait events.
> 
> And msecs_to_jiffies(1000) == HZ.

Agreed. In this first round of cleanup, I chose to keep the primitives as they were in osd.c. Greg, if it is ok with you, I will send you a patch that fixes these issues on top of the patches I have already sent.

Regards,

K. Y
> 
> > @@ -689,7 +693,8 @@ static void vmbus_ongpadl_torndown(
> >  				memcpy(&msginfo->response.gpadl_torndown,
> >  				       gpadl_torndown,
> >  				       sizeof(struct
> vmbus_channel_gpadl_torndown));
> > -				osd_waitevent_set(msginfo->waitevent);
> > +				msginfo->wait_condition = 1;
> > +				wake_up(&msginfo->waitevent);
> >  				break;
> >  			}
> >  		}
> > @@ -730,7 +735,8 @@ static void vmbus_onversion_response(
> >  			memcpy(&msginfo->response.version_response,
> >  			      version_response,
> >  			      sizeof(struct vmbus_channel_version_response));
> > -			osd_waitevent_set(msginfo->waitevent);
> > +			msginfo->wait_condition = 1;
> > +			wake_up(&msginfo->waitevent);
> >  		}
> >  	}
> >  	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
> 
> regards,
> --
> js

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