From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2130.oracle.com ([156.151.31.86]:53764 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727161AbfHHCKv (ORCPT ); Wed, 7 Aug 2019 22:10:51 -0400 Date: Wed, 7 Aug 2019 19:10:46 -0700 From: "Darrick J. Wong" Subject: Re: [PATCH] vfs: fix page locking deadlocks when deduping files Message-ID: <20190808021046.GD7157@magnolia> References: <20190807145114.GP7138@magnolia> <20190807223850.GQ7777@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190807223850.GQ7777@dread.disaster.area> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Dave Chinner Cc: viro@zeniv.linux.org.uk, xfs , linux-fsdevel On Thu, Aug 08, 2019 at 08:38:50AM +1000, Dave Chinner wrote: > On Wed, Aug 07, 2019 at 07:51:14AM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong > > +/* > > + * Lock two pages, ensuring that we lock in offset order if the pages are from > > + * the same file. > > + */ > > +static void vfs_lock_two_pages(struct page *page1, struct page *page2) > > +{ > > + if (page1 == page2) { > > + lock_page(page1); > > + return; > > + } > > + > > + if (page1->mapping == page2->mapping && page1->index > page2->index) > > + swap(page1, page2); > > I would do this even if the pages are on different mappings. That > way we don't expose a landmine if some other code locks two pages > from the same mappings in a different order... Sure. > > + lock_page(page1); > > + lock_page(page2); > > +} > > + > > /* > > * Compare extents of two files to see if they are the same. > > * Caller must have locked both inodes to prevent write races. > > @@ -1867,10 +1881,12 @@ static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff, > > dest_page = vfs_dedupe_get_page(dest, destoff); > > if (IS_ERR(dest_page)) { > > error = PTR_ERR(dest_page); > > - unlock_page(src_page); > > put_page(src_page); > > goto out_error; > > } > > + > > + vfs_lock_two_pages(src_page, dest_page); > > + > > src_addr = kmap_atomic(src_page); > > dest_addr = kmap_atomic(dest_page); > > > > @@ -1882,7 +1898,8 @@ static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff, > > > > kunmap_atomic(dest_addr); > > kunmap_atomic(src_addr); > > - unlock_page(dest_page); > > + if (dest_page != src_page) > > + unlock_page(dest_page); > > unlock_page(src_page); > > Would it make sense for symmetry to wrap these in > vfs_unlock_two_pages()? Sure. --D > -Dave. > -- > Dave Chinner > david@fromorbit.com