linux-kernel - Re: [PATCH -mm] markers: avoid call_rcu

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Message-ID: <20080713042810.GA17339@Krystal>
Date:	Sun, 13 Jul 2008 00:28:11 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Hideo AOKI <haoki@...hat.com>,
	Takahiro Yasui <tyasui@...hat.com>
Subject: Re: [PATCH -mm] markers: avoid call_rcu_sched if old is NULL

* Andrew Morton (akpm@...ux-foundation.org) wrote:
> On Tue, 8 Jul 2008 23:02:01 -0400 Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > * Masami Hiramatsu (mhiramat@...hat.com) wrote:
> > > Introduce marker_entry_free_old() and check old pointer is NULL before
> > > setting call_rcu_sched(), because marker_entry_remove/add_probe() can
> > > return NULL.
> > > 
> > 
> > Hi Masami,
> > 
> > I doubt this is a bug per se, because kfree accepts NULL pointers (and
> > kfree is the only action done on the oldptr by free_old_closure).
> > 
> > This cleans up the code, so I think it's good to merge your patch, but I
> > would definitely not classify this as a bugfix.
> > 
> > Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> 
> I cannot get this to apply on the rather dated tree which I have on this
> rather not-on-the-internet machine.  Please merge this patch locally, test,
> rewrite the changelog and resend it to someone ;)
> 

Hi Andrew,

As I pointed out in a reply to this email, I NACK this patch because it
removes a necessary quiescent state wait from the marker code. The other
reply here explains why I changed my mind about this patch.

http://linux.derkeiler.com/Mailing-Lists/Kernel/2008-07/msg03514.html

Mathieu


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Mathieu Desnoyers
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