linux-kernel - Re: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page replacement.

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Message-ID: <20110315180743.GD24254@linux.vnet.ibm.com>
Date:	Tue, 15 Mar 2011 23:37:43 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>, 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>,
	Andi Kleen <andi@...stfloor.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Oleg Nesterov <oleg@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	SystemTap <systemtap@...rces.redhat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page
 replacement.

* Thomas Gleixner <tglx@...utronix.de> [2011-03-15 19:03:44]:

> On Tue, 15 Mar 2011, Srikar Dronamraju wrote:
> 
> > * Thomas Gleixner <tglx@...utronix.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.

We no more call it write locked. So we can drop the reference to
write lock.
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