From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id C65566B0044 for ; Sat, 5 Dec 2009 07:41:37 -0500 (EST) Date: Sat, 5 Dec 2009 12:41:26 +0000 (GMT) From: Hugh Dickins Subject: Re: [PATCH] hugetlb: Acquire the i_mmap_lock before walking the prio_tree to unmap a page V2 In-Reply-To: <20091202222049.GC26702@csn.ul.ie> Message-ID: References: <20091202222049.GC26702@csn.ul.ie> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Wed, 2 Dec 2009, Mel Gorman wrote: > Changelog since V1 > o Delete stupid comment from the description > > When the owner of a mapping fails COW because a child process is holding > a reference, the children VMAs are walked and the page is unmapped. The > i_mmap_lock is taken for the unmapping of the page but not the walking of > the prio_tree. In theory, that tree could be changing if the lock is not > held. This patch takes the i_mmap_lock properly for the duration of the > prio_tree walk. > > [hugh.dickins@tiscali.co.uk: Spotted the problem in the first place] > Signed-off-by: Mel Gorman Acked-by: Hugh Dickins (and Andrew has already put this version into mmotm, thanks) > --- > mm/hugetlb.c | 9 ++++++++- > 1 files changed, 8 insertions(+), 1 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index a952cb8..5adc284 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1906,6 +1906,12 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma, > + (vma->vm_pgoff >> PAGE_SHIFT); > mapping = (struct address_space *)page_private(page); > > + /* > + * Take the mapping lock for the duration of the table walk. As > + * this mapping should be shared between all the VMAs, > + * __unmap_hugepage_range() is called as the lock is already held > + */ > + spin_lock(&mapping->i_mmap_lock); > vma_prio_tree_foreach(iter_vma, &iter, &mapping->i_mmap, pgoff, pgoff) { > /* Do not unmap the current VMA */ > if (iter_vma == vma) > @@ -1919,10 +1925,11 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma, > * from the time of fork. This would look like data corruption > */ > if (!is_vma_resv_set(iter_vma, HPAGE_RESV_OWNER)) > - unmap_hugepage_range(iter_vma, > + __unmap_hugepage_range(iter_vma, > address, address + huge_page_size(h), > page); > } > + spin_unlock(&mapping->i_mmap_lock); > > return 1; > } -- 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