From patchwork Tue Nov 1 22:36:30 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 9408279 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 B4AC060721 for ; Tue, 1 Nov 2016 22:38:01 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A241629AFF for ; Tue, 1 Nov 2016 22:38:01 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 95F6729B07; Tue, 1 Nov 2016 22:38:01 +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=-1.9 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_NONE autolearn=unavailable version=3.3.1 Received: from ml01.01.org (ml01.01.org [198.145.21.10]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 4DB0829AFF for ; Tue, 1 Nov 2016 22:38:01 +0000 (UTC) Received: from [127.0.0.1] (localhost [IPv6:::1]) by ml01.01.org (Postfix) with ESMTP id 164B381D97; Tue, 1 Nov 2016 15:37:39 -0700 (PDT) X-Original-To: linux-nvdimm@lists.01.org Delivered-To: linux-nvdimm@lists.01.org Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 99A2381D4C for ; Tue, 1 Nov 2016 15:37:36 -0700 (PDT) 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 B47B9ADC8; Tue, 1 Nov 2016 22:37:36 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id BC54A1E0FD2; Tue, 1 Nov 2016 23:37:27 +0100 (CET) From: Jan Kara To: Subject: [PATCH 19/21] dax: Make cache flushing protected by entry lock Date: Tue, 1 Nov 2016 23:36:30 +0100 Message-Id: <1478039794-20253-25-git-send-email-jack@suse.cz> X-Mailer: git-send-email 2.6.6 In-Reply-To: <1478039794-20253-1-git-send-email-jack@suse.cz> References: <1478039794-20253-1-git-send-email-jack@suse.cz> X-BeenThere: linux-nvdimm@lists.01.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Linux-nvdimm developer list." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-fsdevel@vger.kernel.org, Andrew Morton , Jan Kara , linux-nvdimm@lists.01.org MIME-Version: 1.0 Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" 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. Reviewed-by: Ross Zwisler Signed-off-by: Jan Kara --- fs/dax.c | 61 +++++++++++++++++++++++++++++++++++++++---------------------- 1 file changed, 39 insertions(+), 22 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index b4ea4bcca9e7..857117b6db6b 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -619,32 +619,50 @@ 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; - struct radix_tree_node *node; struct blk_dax_ctl dax; - void **slot; + void *entry2, **slot; int ret = 0; - 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_unlocked; + /* + * 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 (dax_radix_sector(entry2) != dax_radix_sector(entry)) + goto put_unlocked; if (WARN_ON_ONCE(dax_is_empty_entry(entry) || dax_is_zero_entry(entry))) { ret = -EIO; - goto unlock; + goto put_unlocked; } + /* Another fsync thread may have already written back this entry */ + if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)) + goto put_unlocked; + /* 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); + /* * Even if dax_writeback_mapping_range() was given a wbc->range_start * in the middle of a PMD, the 'index' we are given will be aligned to @@ -654,15 +672,16 @@ static int dax_writeback_one(struct block_device *bdev, */ dax.sector = dax_radix_sector(entry); dax.size = PAGE_SIZE << dax_radix_order(entry); - spin_unlock_irq(&mapping->tree_lock); /* * We cannot hold tree_lock while calling dax_map_atomic() because it * eventually calls cond_resched(). */ ret = dax_map_atomic(bdev, &dax); - if (ret < 0) + if (ret < 0) { + put_locked_mapping_entry(mapping, index, entry); return ret; + } if (WARN_ON_ONCE(ret < dax.size)) { ret = -EIO; @@ -670,15 +689,13 @@ 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: dax_unmap_atomic(bdev, &dax); + put_locked_mapping_entry(mapping, index, entry); return ret; - unlock: + put_unlocked: + put_unlocked_mapping_entry(mapping, index, entry2); spin_unlock_irq(&mapping->tree_lock); return ret; }