linux-kernel - RE: kref refcnt and false positives

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Message-ID: <EB12A50964762B4D8111D55B764A8454010572C1@scsmsx413.amr.corp.intel.com>
Date:	Thu, 14 Dec 2006 15:51:38 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	"Eric Dumazet" <dada1@...mosbay.com>,
	"Andrew Morton" <akpm@...l.org>
Cc:	"Greg KH" <gregkh@...e.de>, "Arjan" <arjan@...ux.intel.com>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: RE: kref refcnt and false positives

 

>-----Original Message-----
>From: Eric Dumazet [mailto:dada1@...mosbay.com] 
>Sent: Wednesday, December 13, 2006 11:57 PM
>To: Andrew Morton
>Cc: Greg KH; Pallipadi, Venkatesh; Arjan; linux-kernel; Eric 
>W. Biederman
>Subject: Re: kref refcnt and false positives
>
>
>I agree this 'optimization' is not "good" (I was the guy who 
>suggested it 
>http://lkml.org/lkml/2006/1/30/4 )
>
>After Eric Biederman message 
>(http://lkml.org/lkml/2006/1/30/292) I remember 
>adding some stat counters and telling Greg to not put the 
>patch in because 
>kref_put() was mostly called with refcount=1. But the patch 
>did its way. I 
>*did* ask Greg to revert it, but cannot find this mail 
>archived somewhere...
>
>But I believe Venkatesh problem comes from its release() 
>function : It is 
>supposed to free the object.
>If not, it should properly setup it so that further uses are OK.
>
>ie doing in release(kref)
>atomic_set(&kref->count, 0);
>

Agreed that setting kref refcnt to 0 in release will solve the probloem.
But, once the optimization code is removed, we don't need to set it to
zero as release will only be called after the count reaches zero anyway.

Thanks,
Venki
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