linux-kernel - Re: [RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu

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Message-ID: <20120414205200.GA9083@redhat.com>
Date:	Sat, 14 Apr 2012 22:52:00 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Anton Arapov <anton@...hat.com>
Subject: Re: [RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu_id

On 04/14, Peter Zijlstra wrote:
>
> On Fri, 2012-04-06 at 00:20 +0200, Oleg Nesterov wrote:
> > Hello.
> >
> > Not for inclusion yet, only for the early review.
> >
> > I didn't even try to test these changes, and I am not expert
> > in this area. And even _if_ this code is correct, I need to
> > re-split these changes anyway, update the changelogs, etc.
> >
> > Questions:
> >
> > 	- does it make sense?
>
> Maybe, upside is reclaiming that int from task_struct, downside is that
> down_write :/ It would be very good not to have to do that.

Yes, down_write() is pessimization, I agree.

> Nor do I
> really see how that works.
>
> > 	- can it work or I missed something "in general" ?
>
> So we insert in the rb-tree before we take mmap_sem, this means we can
> hit a non-uprobe int3 and still find a uprobe there, no?

Yes, but unless I miss something this is "off-topic", this
can happen with or without these changes. If find_uprobe()
succeeds we assume that this bp was inserted by uprobe.

Perhaps uprobe_register() should not "ignore" -EXIST from
install_breakpoint()->is_swbp_insn(), or perhaps we can
add UPROBE_SHARED_BP.

Oleg.

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