linux-kernel - Re: [PATCH 6/7] uprobes: Do not allocate current->utask unnecessary

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Message-ID: <20130108181303.GB1048@redhat.com>
Date:	Tue, 8 Jan 2013 19:13:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Josh Stone <jistone@...hat.com>,
	"Suzuki K. Poulose" <suzuki@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] uprobes: Do not allocate current->utask unnecessary

On 01/08, Srikar Dronamraju wrote:
>
> * Oleg Nesterov <oleg@...hat.com> [2012-12-31 18:52:29]:
>
> >  static void handle_swbp(struct pt_regs *regs)
> >  {
> > -	struct uprobe_task *utask;
> >  	struct uprobe *uprobe;
> >  	unsigned long bp_vaddr;
> >  	int uninitialized_var(is_swbp);
> > @@ -1512,19 +1515,12 @@ static void handle_swbp(struct pt_regs *regs)
> >  	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
> >  		goto out;
> >
> > -	utask = get_utask();
> > -	if (!utask)
> > -		goto out;	/* re-execute the instruction. */
> > -
>
> If get_utask fails with the above change, Dont we end up calling
> handler_chain twice(or more)?.

After restart, yes.

> I think this is probably true with
> previous patch too.

And this can happen with the current code too, if xol_alloc_area()
fails. So I think this is probably fine. Besides, if GFP_KERNEL
fails the task should be oom-killed in practice.

Oleg.

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