linux-kernel - Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.

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Date:	Wed, 26 Jan 2011 13:25:58 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 5/20]  5: Uprobes:
 register/unregister probes.

> > +
> > +               list_add(&mm->uprobes_list, &tmp_list);
> > +               mm->uprobes_vaddr = vma->vm_start + offset;
> > +       }
> > +       spin_unlock(&mapping->i_mmap_lock);
> 
> Both this and unregister are racy, what is to say:
>  - the vma didn't get removed from the mm
>  - no new matching vma got added
> 

register_uprobe, unregister_uprobe, uprobe_mmap are all synchronized by
uprobes_mutex. So I dont see one unregister_uprobe getting thro when
another register_uprobe is working with a vma.

If I am missing something elementary, please explain a bit more.

> > +       if (list_empty(&tmp_list)) {
> > +               ret = 0;
> > +               goto consumers_add;
> > +       }
> > +       list_for_each_entry_safe(mm, tmpmm, &tmp_list, uprobes_list) {
> > +               if (!install_uprobe(mm, uprobe))
> > +                       ret = 0;
> > +               list_del(&mm->uprobes_list);
> > +               mmput(mm);
> > +       }
> > +
> > +consumers_add:
> > +       add_consumer(uprobe, consumer);
> > +       mutex_unlock(&uprobes_mutex);
> > +       put_uprobe(uprobe);
> > +       return ret;
> > +}
> > + 

-- 
Thanks and Regards
Srikar
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