From patchwork Tue Jun 21 15:45:13 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 9190943 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id D10A26089F for ; Tue, 21 Jun 2016 16:34:02 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C10C72807B for ; Tue, 21 Jun 2016 16:34:02 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B517E282ED; Tue, 21 Jun 2016 16:34:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 368F1280F4 for ; Tue, 21 Jun 2016 16:34:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752621AbcFUQdu (ORCPT ); Tue, 21 Jun 2016 12:33:50 -0400 Received: from mx2.suse.de ([195.135.220.15]:43771 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752476AbcFUQdt (ORCPT ); Tue, 21 Jun 2016 12:33:49 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id C5F85AD9E; Tue, 21 Jun 2016 15:45:22 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id E56A41E0728; Tue, 21 Jun 2016 17:45:21 +0200 (CEST) From: Jan Kara To: linux-nvdimm@lists.01.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Dan Williams , Ross Zwisler , Jan Kara Subject: [PATCH 1/3] dax: Make cache flushing protected by entry lock Date: Tue, 21 Jun 2016 17:45:13 +0200 Message-Id: <1466523915-14644-2-git-send-email-jack@suse.cz> X-Mailer: git-send-email 2.6.6 In-Reply-To: <1466523915-14644-1-git-send-email-jack@suse.cz> References: <1466523915-14644-1-git-send-email-jack@suse.cz> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Currently, flushing of caches for DAX mappings was ignoring entry lock. So far this was ok (modulo a bug that a difference in entry lock could cause cache flushing to be mistakenly skipped) but in the following patches we will write-protect PTEs on cache flushing and clear dirty tags. For that we will need more exclusion. So do cache flushing under an entry lock. This allows us to remove one lock-unlock pair of mapping->tree_lock as a bonus. Signed-off-by: Jan Kara --- fs/dax.c | 62 +++++++++++++++++++++++++++++++++++++++----------------------- 1 file changed, 39 insertions(+), 23 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 761495bf5eb9..5209f8cd0bee 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -669,35 +669,54 @@ static int dax_writeback_one(struct block_device *bdev, struct address_space *mapping, pgoff_t index, void *entry) { struct radix_tree_root *page_tree = &mapping->page_tree; - int type = RADIX_DAX_TYPE(entry); - struct radix_tree_node *node; + int type; struct blk_dax_ctl dax; - void **slot; int ret = 0; + void *entry2, **slot; - spin_lock_irq(&mapping->tree_lock); /* - * Regular page slots are stabilized by the page lock even - * without the tree itself locked. These unlocked entries - * need verification under the tree lock. + * A page got tagged dirty in DAX mapping? Something is seriously + * wrong. */ - if (!__radix_tree_lookup(page_tree, index, &node, &slot)) - goto unlock; - if (*slot != entry) - goto unlock; - - /* another fsync thread may have already written back this entry */ - if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)) - goto unlock; + if (WARN_ON(!radix_tree_exceptional_entry(entry))) + return -EIO; + spin_lock_irq(&mapping->tree_lock); + entry2 = get_unlocked_mapping_entry(mapping, index, &slot); + /* Entry got punched out / reallocated? */ + if (!entry2 || !radix_tree_exceptional_entry(entry2)) + goto put_unlock; + /* + * Entry got reallocated elsewhere? No need to writeback. We have to + * compare sectors as we must not bail out due to difference in lockbit + * or entry type. + */ + if (RADIX_DAX_SECTOR(entry2) != RADIX_DAX_SECTOR(entry)) + goto put_unlock; + type = RADIX_DAX_TYPE(entry2); if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) { ret = -EIO; - goto unlock; + goto put_unlock; } + entry = entry2; + + /* Another fsync thread may have already written back this entry */ + if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)) + goto put_unlock; + /* Lock the entry to serialize with page faults */ + entry = lock_slot(mapping, slot); + /* + * We can clear the tag now but we have to be careful so that concurrent + * dax_writeback_one() calls for the same index cannot finish before we + * actually flush the caches. This is achieved as the calls will look + * at the entry only under tree_lock and once they do that they will + * see the entry locked and wait for it to unlock. + */ + radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE); + spin_unlock_irq(&mapping->tree_lock); dax.sector = RADIX_DAX_SECTOR(entry); dax.size = (type == RADIX_DAX_PMD ? PMD_SIZE : PAGE_SIZE); - spin_unlock_irq(&mapping->tree_lock); /* * We cannot hold tree_lock while calling dax_map_atomic() because it @@ -713,15 +732,12 @@ static int dax_writeback_one(struct block_device *bdev, } wb_cache_pmem(dax.addr, dax.size); - - spin_lock_irq(&mapping->tree_lock); - radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE); - spin_unlock_irq(&mapping->tree_lock); - unmap: +unmap: dax_unmap_atomic(bdev, &dax); return ret; - unlock: +put_unlock: + put_unlocked_mapping_entry(mapping, index, entry2); spin_unlock_irq(&mapping->tree_lock); return ret; }