Date: Sat, 28 Sep 2013 21:46:49 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Waiman Long <Waiman.Long@hp.com>, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@redhat.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        Davidlohr Bueso <davidlohr.bueso@hp.com>,
        Alex Shi <alex.shi@intel.com>, Tim Chen <tim.c.chen@linux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Matthew R Wilcox <matthew.r.wilcox@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Michel Lespinasse <walken@google.com>,
        Andi Kleen <andi@firstfloor.org>,
        "Chandramouleeswaran, Aswin" <aswin@hp.com>,
        "Norton, Scott J" <scott.norton@hp.com>
Subject: Re: [PATCH] anon_vmas: Convert the rwsem to an rwlock_t
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Sat, Sep 28, 2013 at 12:37 PM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > -               down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem);
> > +               down_write_nest_lock(&anon_vma->root->rwlock, &mm->mmap_sem);
> 
> That's just completely bogus, and cannot work.

Told you it's totally untested :-) Found that build failure a few minutes 
ago (the place escaped my search pattern), I'm trying the fix below.

	Ingo

diff --git a/mm/mmap.c b/mm/mmap.c
index 25ce233..7ee85bf 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2955,7 +2955,7 @@ static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
 		 * The LSB of head.next can't change from under us
 		 * because we hold the mm_all_locks_mutex.
 		 */
-		down_write_nest_lock(&anon_vma->root->rwlock, &mm->mmap_sem);
+		write_lock(&anon_vma->root->rwlock);
 		/*
 		 * We can safely modify head.next after taking the
 		 * anon_vma->root->rwlock. If some other vma in this mm shares
--
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