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Date: Wed, 5 Oct 2011 18:19:14 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        Steven Rostedt <rostedt@goodmis.org>, Linux-mm <linux-mm@kvack.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>, Hugh Dickins <hughd@google.com>,
        Christoph Hellwig <hch@infradead.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Thomas Gleixner <tglx@linutronix.de>, Andi Kleen <andi@firstfloor.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Roland McGrath <roland@hack.frob.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 9/26]   Uprobes: Background page
	replacement.
Message-ID: <20111005161914.GA903@redhat.com>
References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com> <20110920120137.25326.72005.sendpatchset@srdronam.in.ibm.com>
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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.