linux-kernel - Re: [PATCH 12/13] tracing/uprobes: Add more fetch functions

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Date:	Mon, 04 Nov 2013 17:50:53 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei\(Jovi\)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 12/13] tracing/uprobes: Add more fetch functions

On Thu, 31 Oct 2013 19:22:18 +0100, Oleg Nesterov wrote:
> On 10/29, Namhyung Kim wrote:
>>
>> +static void __user *get_user_vaddr(unsigned long addr, struct trace_uprobe *tu)
>> +{
>> +	unsigned long pgoff = addr >> PAGE_SHIFT;
>> +	struct vm_area_struct *vma;
>> +	struct address_space *mapping;
>> +	unsigned long vaddr = 0;
>> +
>> +	if (tu == NULL) {
>> +		/* A NULL tu means that we already got the vaddr */
>> +		return (void __force __user *) addr;
>> +	}
>> +
>> +	mapping = tu->inode->i_mapping;
>> +
>> +	mutex_lock(&mapping->i_mmap_mutex);
>> +	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
>> +		if (vma->vm_mm != current->mm)
>> +			continue;
>> +		if (!(vma->vm_flags & VM_READ))
>> +			continue;
>> +
>> +		vaddr = offset_to_vaddr(vma, addr);
>> +		break;
>> +	}
>> +	mutex_unlock(&mapping->i_mmap_mutex);
>> +
>> +	WARN_ON_ONCE(vaddr == 0);
>
> Hmm. But unless I missed something this "addr" passed as an argument can
> be wrong? And if nothing else this or another thread can unmap the vma?

You mean WARN_ON_ONCE here is superfluous?  I admit that it should
protect concurrent vma [un]mappings.  Please see my reply in other
thread for a new approach.

Thanks,
Namhyung
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