From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f170.google.com (mail-pd0-f170.google.com [209.85.192.170]) by kanga.kvack.org (Postfix) with ESMTP id 231CC6B0069 for ; Thu, 23 Oct 2014 07:03:53 -0400 (EDT) Received: by mail-pd0-f170.google.com with SMTP id z10so836255pdj.29 for ; Thu, 23 Oct 2014 04:03:52 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id qo15si1319672pab.123.2014.10.23.04.03.51 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Oct 2014 04:03:52 -0700 (PDT) Date: Thu, 23 Oct 2014 13:03:46 +0200 From: Peter Zijlstra Subject: Re: [RFC][PATCH 4/6] SRCU free VMAs Message-ID: <20141023110346.GP21513@worktop.programming.kicks-ass.net> References: <20141020215633.717315139@infradead.org> <20141020222841.419869904@infradead.org> <5448D515.90006@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5448D515.90006@cn.fujitsu.com> Sender: owner-linux-mm@kvack.org List-ID: To: Lai Jiangshan Cc: torvalds@linux-foundation.org, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, akpm@linux-foundation.org, riel@redhat.com, mgorman@suse.de, oleg@redhat.com, mingo@redhat.com, minchan@kernel.org, kamezawa.hiroyu@jp.fujitsu.com, viro@zeniv.linux.org.uk, dave@stgolabs.net, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Thu, Oct 23, 2014 at 06:14:45PM +0800, Lai Jiangshan wrote: > > > > > +struct vm_area_struct *find_vma_srcu(struct mm_struct *mm, unsigned long addr) > > +{ > > + struct vm_area_struct *vma; > > + unsigned int seq; > > + > > + WARN_ON_ONCE(!srcu_read_lock_held(&vma_srcu)); > > + > > + do { > > + seq = read_seqbegin(&mm->mm_seq); > > + vma = __find_vma(mm, addr); > > will the __find_vma() loops for ever due to the rotations in the RBtree? No, a rotation takes a tree and generates a tree, furthermore the rotation has a fairly strict fwd progress guarantee seeing how its now done with preemption disabled. Therefore, even if we're in a node that's being rotated up, we can only 'loop' for as long as it takes for the new pointer stores to become visible on our CPU. Thus we have a tree descent termination guarantee. -- 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/ . Don't email: email@kvack.org