linux-kernel - Re: [PATCH] anon_vmas: Convert the rwsem to an rwlock

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Message-ID: <20130928194649.GB8640@gmail.com>
Date:	Sat, 28 Sep 2013 21:46:49 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Waiman Long <Waiman.Long@...com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Alex Shi <alex.shi@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [PATCH] anon_vmas: Convert the rwsem to an rwlock_t


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Sat, Sep 28, 2013 at 12:37 PM, Ingo Molnar <mingo@...nel.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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