Date: Tue, 15 Mar 2011 19:03:44 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        Steven Rostedt <rostedt@goodmis.org>, Linux-mm <linux-mm@kvack.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Christoph Hellwig <hch@infradead.org>,
        Andi Kleen <andi@firstfloor.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Oleg Nesterov <oleg@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Roland McGrath <roland@hack.frob.com>,
        SystemTap <systemtap@sources.redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page
 replacement.
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On Tue, 15 Mar 2011, Srikar Dronamraju wrote:

> * Thomas Gleixner <tglx@linutronix.de> [2011-03-15 14:22:09]:
> 
> > On Mon, 14 Mar 2011, Srikar Dronamraju wrote:
> > > +/*
> > > + * Called with tsk->mm->mmap_sem held (either for read or write and
> > > + * with a reference to tsk->mm
> > 
> > Hmm, why is holding it for read sufficient?
> 
> We are not adding a new vma to the mm; but just replacing a page with
> another after holding the locks for the pages. Existing routines
> doing close to similar things like the
> access_process_vm/get_user_pages seem to be taking the read_lock. Do
> you see a resaon why readlock wouldnt suffice?

No, I just was confused by the comment. Probably should have asked why
you want to call it write locked.
 
Thanks,

	tglx
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