From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:50506 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727147AbfACOaE (ORCPT ); Thu, 3 Jan 2019 09:30:04 -0500 Date: Thu, 3 Jan 2019 09:29:59 -0500 From: Jerome Glisse Subject: Re: [PATCH] Initialise mmu_notifier_range correctly Message-ID: <20190103142959.GA3395@redhat.com> References: <20190103002126.GM6310@bombadil.infradead.org> <20190103015654.GB15619@redhat.com> <785af237-eb67-c304-595d-9080a2f48102@nvidia.com> <20190103041833.GN6310@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190103041833.GN6310@bombadil.infradead.org> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Matthew Wilcox Cc: John Hubbard , Andrew Morton , linux-mm@kvack.org, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Christian =?iso-8859-1?Q?K=F6nig?= , Jan Kara On Wed, Jan 02, 2019 at 08:18:33PM -0800, Matthew Wilcox wrote: > On Wed, Jan 02, 2019 at 07:32:08PM -0800, John Hubbard wrote: > > Having the range struct declared in separate places from the mmu_notifier_range_init() > > calls is not great. But I'm not sure I see a way to make it significantly cleaner, given > > that __follow_pte_pmd uses the range pointer as a way to decide to issue the mmn calls. > > Yeah, I don't think there's anything we can do. But I started reviewing > the comments, and they don't make sense together: > > /* > * Note because we provide range to follow_pte_pmd it will > * call mmu_notifier_invalidate_range_start() on our behalf > * before taking any lock. > */ > if (follow_pte_pmd(vma->vm_mm, address, &range, > &ptep, &pmdp, &ptl)) > continue; > > /* > * No need to call mmu_notifier_invalidate_range() as we are > * downgrading page table protection not changing it to point > * to a new page. > * > * See Documentation/vm/mmu_notifier.rst > */ > > So if we don't call mmu_notifier_invalidate_range, why are we calling > mmu_notifier_invalidate_range_start and mmu_notifier_invalidate_range_end? > ie, why not this ... Thus comments looks wrong to me ... we need to call mmu_notifier_invalidate_range() those are use by IOMMU. I might be to blame for those comments thought. > > diff --git a/fs/dax.c b/fs/dax.c > index 6959837cc465..905340149924 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -777,7 +777,6 @@ static void dax_entry_mkclean(struct address_space *mapping, pgoff_t index, > > i_mmap_lock_read(mapping); > vma_interval_tree_foreach(vma, &mapping->i_mmap, index, index) { > - struct mmu_notifier_range range; > unsigned long address; > > cond_resched(); > @@ -787,12 +786,7 @@ static void dax_entry_mkclean(struct address_space *mapping, pgoff_t index, > > address = pgoff_address(index, vma); > > - /* > - * Note because we provide start/end to follow_pte_pmd it will > - * call mmu_notifier_invalidate_range_start() on our behalf > - * before taking any lock. > - */ > - if (follow_pte_pmd(vma->vm_mm, address, &range, > + if (follow_pte_pmd(vma->vm_mm, address, NULL, > &ptep, &pmdp, &ptl)) > continue; > > @@ -834,8 +828,6 @@ static void dax_entry_mkclean(struct address_space *mapping, pgoff_t index, > unlock_pte: > pte_unmap_unlock(ptep, ptl); > } > - > - mmu_notifier_invalidate_range_end(&range); > } > i_mmap_unlock_read(mapping); > }