From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id D54296B0092 for ; Mon, 24 Jan 2011 07:21:19 -0500 (EST) Subject: Re: [PATCH 00/21] mm: Preemptibility -v6 From: Peter Zijlstra In-Reply-To: <1295624034.28776.303.camel@laptop> References: <20101126143843.801484792@chello.nl> <1295457039.28776.137.camel@laptop> <1295624034.28776.303.camel@laptop> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Date: Mon, 24 Jan 2011 13:21:54 +0100 Message-ID: <1295871714.28776.406.camel@laptop> Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: Andrew Morton , Benjamin Herrenschmidt , David Miller , Nick Piggin , Martin Schwidefsky , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Andrea Arcangeli , Oleg Nesterov , "Paul E. McKenney" List-ID: On Fri, 2011-01-21 at 16:33 +0100, Peter Zijlstra wrote: > Index: linux-2.6/mm/rmap.c > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > --- linux-2.6.orig/mm/rmap.c > +++ linux-2.6/mm/rmap.c > @@ -1559,9 +1559,20 @@ void __put_anon_vma(struct anon_vma *ano > * Synchronize against page_lock_anon_vma() such that > * we can safely hold the lock without the anon_vma getting > * freed. > + * > + * Relies on the full mb implied by the atomic_dec_and_test() from > + * put_anon_vma() against the full mb implied by mutex_trylock() from > + * page_lock_anon_vma(). This orders: > + * > + * page_lock_anon_vma() VS put_anon_vma() > + * mutex_trylock() atomic_dec_and_test() > + * smp_mb() smp_mb() > + * atomic_read() mutex_is_locked() Bah!, I thought all mutex_trylock() implementations used an atomic op with return value (which implies a mb), but it looks like (at least*) PPC doesn't and only provides a LOCK barrier. * possibly ARM and SH don't either, but I can't read either ASMs well enough to tell. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org