linux-kernel - Re: [PATCH v4 3.0-rc2-tip 4/22] 4: Uprobes: register/unregister probes.

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Date:	Thu, 16 Jun 2011 11:10:22 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.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>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3.0-rc2-tip 4/22]  4: Uprobes: register/unregister
 probes.

* Peter Zijlstra <peterz@...radead.org> [2011-06-10 01:03:24]:

> On Tue, 2011-06-07 at 18:29 +0530, Srikar Dronamraju wrote:
> > +       vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, 0) {
> > +               loff_t vaddr;
> > +               struct task_struct *tsk;
> > +
> > +               if (!atomic_inc_not_zero(&vma->vm_mm->mm_users))
> > +                       continue;
> > +
> > +               mm = vma->vm_mm;
> > +               if (!valid_vma(vma)) {
> > +                       mmput(mm);
> > +                       continue;
> > +               }
> > +
> > +               vaddr = vma->vm_start + offset;
> > +               vaddr -= vma->vm_pgoff << PAGE_SHIFT;
> > +               if (vaddr < vma->vm_start || vaddr > vma->vm_end) {
> > +                       /* Not in this vma */
> > +                       mmput(mm);
> > +                       continue;
> > +               }
> > +               tsk = get_mm_owner(mm);
> > +               if (tsk && vaddr > TASK_SIZE_OF(tsk)) {
> > +                       /*
> > +                        * We cannot have a virtual address that is
> > +                        * greater than TASK_SIZE_OF(tsk)
> > +                        */
> > +                       put_task_struct(tsk);
> > +                       mmput(mm);
> > +                       continue;
> > +               }
> > +               put_task_struct(tsk);
> > +               mm->uprobes_vaddr = (unsigned long) vaddr;
> > +               list_add(&mm->uprobes_list, &try_list);
> > +       } 
> 
> This still falls flat on its face when there's multiple maps of the same
> text in one mm.
> 

To address this we will use a uprobe_info structure.

struct uprobe_info {
        unsigned long uprobes_vaddr;
        struct mm_struct *mm;
        struct list_head uprobes_list;
};

and remove the uprobes_list and uprobes_vaddr entries from mm structure.

the uprobe_info structures will be created in the vma_prio_tree_foreach
loop as and when required. Since we now have i_mmap_mutex, allocating this
uprobe_info structure as when required should be okay.

Agree?

-- 
Thanks and Regards
Srikar
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