linux-kernel - Re: [RFC] [PATCH 2.6.37-rc5-tip 14/20] 14: uprobes: Handing int3 and singlestep exception.

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Date:	Wed, 26 Jan 2011 11:17:11 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	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>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 14/20] 14: uprobes: Handing int3
 and singlestep exception.

On Wed, 2011-01-26 at 14:22 +0530, Srikar Dronamraju wrote:
> * Peter Zijlstra <peterz@...radead.org> [2011-01-25 14:56:19]:
> 
> > On Thu, 2010-12-16 at 15:29 +0530, Srikar Dronamraju wrote:
> > > +               down_read(&mm->mmap_sem);
> > > +               for (vma = mm->mmap; vma; vma = vma->vm_next) {
> > > +                       if (!valid_vma(vma))
> > > +                               continue;
> > > +                       if (probept < vma->vm_start || probept > vma->vm_end)
> > > +                               continue;
> > > +                       u = find_uprobe(vma->vm_file->f_mapping->host,
> > > +                                       probept - vma->vm_start);
> > > +                       if (u)
> > > +                               break;
> > > +               }
> > > +               up_read(&mm->mmap_sem); 
> > 
> > One has to ask, what's wrong with find_vma() ?
> 
> Are you looking for something like this.
> 
>        down_read(&mm->mmap_sem);
> 	for (vma = find_vma(mm, probept); ; vma = vma->vm_next) {
> 	       if (!valid_vma(vma))
> 		       continue;
> 	       u = find_uprobe(vma->vm_file->f_mapping->host,
> 			       probept - vma->vm_start);
> 	       if (u)
> 		       break;
>        }
>        up_read(&mm->mmap_sem); 

How could you ever need to iterate here? There is only a single vma that
covers the probe point, if that doesn't find a uprobe, there isn't any.
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