netdev - Re: [PATCH] kref: add function for reading kref value

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Message-ID: <1323712663.2583.16.camel@edumazet-laptop>
Date:	Mon, 12 Dec 2011 18:57:43 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Baluta <dbaluta@...acom.com>
Cc:	Greg KH <greg@...ah.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, adobriyan@...il.com
Subject: Re: [PATCH] kref: add function for reading kref value

Le lundi 12 décembre 2011 à 19:46 +0200, Daniel Baluta a écrit :
> On Mon, Dec 12, 2011 at 7:33 PM, Greg KH <greg@...ah.com> wrote:
> > On Mon, Dec 12, 2011 at 06:42:59PM +0200, Daniel Baluta wrote:
> >> On Mon, Dec 12, 2011 at 5:41 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >> > Le lundi 12 décembre 2011 ŕ 17:39 +0200, Daniel Baluta a écrit :
> >> >
> >> >> Ok, for the moment it seems to be a bad idea. But my intention is
> >> >> to integrate kref to networking code, and then to write a general
> >> >> debugging tool for refs.
> >> >>
> >> >> Tracking down reference count problems is hard, and this tool can
> >> >> really help everyone.
> >> >
> >> > I dont think kref will help you that much, because its used everywhere.
> >> >
> >> > Adding a general debugging tool will provide too much noise.
> >> >
> >> > Instead, we (network dev) add debugging points where we want.
> >>
> >> Yes, but you have to do this each time you start debugging, for a
> >> particular referenced counted object.
> >>
> >> We must find a clever solution to avoid the noise. (e.g use
> >> /proc, /sysfs, /debugfs options to trigger dumping info for
> >> some/all objects with a certain state).
> >
> > Then use the dynamic debug infrastructure, which is there to help you
> > try to handle this type of debugging on-the-fly.
> >
> > But again, it's not a kref issue, sorry.
> 
> I see. Thanks.
> 
> One last remark: Should we encourage people
> to use kref implementation, instead of making
> their own ?
> 
> What are the chances of accepting changes with
> respect to this?
> 
> Just a few examples:
> 
> neighbour.h
> 295:#define neigh_hold(n)	atomic_inc(&(n)->refcnt)
> 
> addrconf.h
> 219:static inline void in6_dev_hold(struct inet6_dev *idev)
> 

I dont know how to say this Daniel.

I dont think kref added layer is helping this. Just say no.

Since we convert about all network stack to RCU, we need much better api
than kref is offering.

(atomic_..._not_zero for example)



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