linux-kernel - Re: [PATCH 2/3] tracing/stack-tracer: fix locking

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Message-ID: <49293777.8070404@gmail.com>
Date:	Sun, 23 Nov 2008 12:59:03 +0200
From:	Török Edwin <edwintorok@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	srostedt@...hat.com, a.p.zijlstra@...llo.nl, sandmann@...mi.au.dk,
	linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk
Subject: Re: [PATCH 2/3] tracing/stack-tracer: fix locking

On 2008-11-23 12:52, Ingo Molnar wrote:
> * Török Edwin <edwintorok@...il.com> wrote:
>
>   
>> +		down_read(&mm->mmap_sem);
>> +		vma = find_vma(mm, ip);
>>  		if (vma) {
>>  			file = vma->vm_file;
>>  			vmstart = vma->vm_start;
>>  		}
>> +		up_read(&mm->mmap_sem);
>>  	}
>>  	if (file) {
>>  		ret = trace_seq_path(s, &file->f_path);
>>     
>
> and now it's "file" that is held without a reference and possibly 
> racy.
>   

I'll move the (file) inside the mmap_sem too, since file is part of vma,
and you need mmap_sem to access the vma
nobody can modify (file) if they don't hold mmap_sem.
Am I right?

--Edwin
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