linux-kernel - Re: [PATCH v5 3.1.0-rc4-tip 9/26] Uprobes: Background page replacement.

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Message-ID: <20111005161914.GA903@redhat.com>
Date:	Wed, 5 Oct 2011 18:19:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 9/26]   Uprobes: Background page
	replacement.

On 09/20, Srikar Dronamraju wrote:
>
> +int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr,
> +						uprobe_opcode_t *opcode)
> +{
> +	struct vm_area_struct *vma;
> +	struct page *page;
> +	void *vaddr_new;
> +	int ret;
> +
> +	ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &page, &vma);
> +	if (ret <= 0)
> +		return ret;
> +	ret = -EINVAL;
> +
> +	/*
> +	 * We are interested in text pages only. Our pages of interest
> +	 * should be mapped for read and execute only. We desist from
> +	 * adding probes in write mapped pages since the breakpoints
> +	 * might end up in the file copy.
> +	 */
> +	if (!valid_vma(vma))
> +		goto put_out;

Another case when valid_vma() looks suspicious. We are going to restore
the original instruction. We shouldn't fail (at least we shouldn't "leak"
->mm_uprobes_count) if ->vm_flags was changed between register_uprobe()
and unregister_uprobe().

Oleg.

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