Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752395AbdGESur (ORCPT ); Wed, 5 Jul 2017 14:50:47 -0400 Received: from merlin.infradead.org ([205.233.59.134]:34418 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752092AbdGESup (ORCPT ); Wed, 5 Jul 2017 14:50:45 -0400 Date: Wed, 5 Jul 2017 20:50:23 +0200 From: Peter Zijlstra To: Laurent Dufour Cc: paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen Subject: Re: [RFC v5 09/11] mm: Try spin lock in speculative path Message-ID: <20170705185023.xlqko7wgepwsny5g@hirez.programming.kicks-ass.net> References: <1497635555-25679-1-git-send-email-ldufour@linux.vnet.ibm.com> <1497635555-25679-10-git-send-email-ldufour@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1497635555-25679-10-git-send-email-ldufour@linux.vnet.ibm.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1110 Lines: 32 On Fri, Jun 16, 2017 at 07:52:33PM +0200, Laurent Dufour wrote: > @@ -2294,8 +2295,19 @@ static bool pte_map_lock(struct vm_fault *vmf) > if (vma_has_changed(vmf->vma, vmf->sequence)) > goto out; > > - pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, > - vmf->address, &ptl); > + /* Same as pte_offset_map_lock() except that we call comment style.. > + * spin_trylock() in place of spin_lock() to avoid race with > + * unmap path which may have the lock and wait for this CPU > + * to invalidate TLB but this CPU has irq disabled. > + * Since we are in a speculative patch, accept it could fail > + */ > + ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd); > + pte = pte_offset_map(vmf->pmd, vmf->address); > + if (unlikely(!spin_trylock(ptl))) { > + pte_unmap(pte); > + goto out; > + } > + > if (vma_has_changed(vmf->vma, vmf->sequence)) { > pte_unmap_unlock(pte, ptl); > goto out; Right, so if you look at my earlier patches you'll see I did something quite disgusting here. Not sure that wants repeating, but I cannot remember why I thought this deadlock didn't exist anymore.