From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF753C76186 for ; Wed, 24 Jul 2019 20:23:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A6C912081B for ; Wed, 24 Jul 2019 20:23:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563999830; bh=1W+7OgriDVOasQo5rik9NDAqPm8JRrtdBznRhjpdxHU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=sUf/7BEP0t3DiF3P7TV9RpfqLhl0OShGhIjBrrPwdd19Qgp0RTqZFWD1lbk13X1NG mlLNc5ADE8lJACgYjTb3R1bdgapyGVErWsQJkSWvzCli/UIec63sAnnh4nAr2Sb1Sb 4IEsSfDVOghgmtcm4fl1ru83WSO8V5bND+1ijJpU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388569AbfGXTmR (ORCPT ); Wed, 24 Jul 2019 15:42:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:43886 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389866AbfGXTmR (ORCPT ); Wed, 24 Jul 2019 15:42:17 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 599A1229F4; Wed, 24 Jul 2019 19:42:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563997335; bh=1W+7OgriDVOasQo5rik9NDAqPm8JRrtdBznRhjpdxHU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bjfMAO3e1XxDhSHz+NpICK4XDnoGt/UNiCYkdYeTdWeHI9Iy7YWeeZhT+ha76ivYL RQv9oacBGxEWOhIjR/kWrc/bkqAicrG8MW5N0QAdg30VyzVnms5bphDf5BjIBJUskT 0nzyGY/qae7ozh3r4wAou4sG0oBeTRwjKgTh+JrA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Matthew Wilcox (Oracle)" , Dan Williams , Robert Barror , Seema Pandit , Jan Kara Subject: [PATCH 5.2 402/413] dax: Fix missed wakeup with PMD faults Date: Wed, 24 Jul 2019 21:21:33 +0200 Message-Id: <20190724191803.534561406@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190724191735.096702571@linuxfoundation.org> References: <20190724191735.096702571@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Matthew Wilcox (Oracle) commit 23c84eb7837514e16d79ed6d849b13745e0ce688 upstream. RocksDB can hang indefinitely when using a DAX file. This is due to a bug in the XArray conversion when handling a PMD fault and finding a PTE entry. We use the wrong index in the hash and end up waiting on the wrong waitqueue. There's actually no need to wait; if we find a PTE entry while looking for a PMD entry, we can return immediately as we know we should fall back to a PTE fault (which may not conflict with the lock held). We reuse the XA_RETRY_ENTRY to signal a conflicting entry was found. This value can never be found in an XArray while holding its lock, so it does not create an ambiguity. Cc: Link: http://lkml.kernel.org/r/CAPcyv4hwHpX-MkUEqxwdTj7wCCZCN4RV-L4jsnuwLGyL_UEG4A@mail.gmail.com Fixes: b15cd800682f ("dax: Convert page fault handlers to XArray") Signed-off-by: Matthew Wilcox (Oracle) Tested-by: Dan Williams Reported-by: Robert Barror Reported-by: Seema Pandit Reviewed-by: Jan Kara Signed-off-by: Dan Williams Signed-off-by: Greg Kroah-Hartman --- fs/dax.c | 53 +++++++++++++++++++++++++++++++++-------------------- 1 file changed, 33 insertions(+), 20 deletions(-) --- a/fs/dax.c +++ b/fs/dax.c @@ -124,6 +124,15 @@ static int dax_is_empty_entry(void *entr } /* + * true if the entry that was found is of a smaller order than the entry + * we were looking for + */ +static bool dax_is_conflict(void *entry) +{ + return entry == XA_RETRY_ENTRY; +} + +/* * DAX page cache entry locking */ struct exceptional_entry_key { @@ -195,11 +204,13 @@ static void dax_wake_entry(struct xa_sta * Look up entry in page cache, wait for it to become unlocked if it * is a DAX entry and return it. The caller must subsequently call * put_unlocked_entry() if it did not lock the entry or dax_unlock_entry() - * if it did. + * if it did. The entry returned may have a larger order than @order. + * If @order is larger than the order of the entry found in i_pages, this + * function returns a dax_is_conflict entry. * * Must be called with the i_pages lock held. */ -static void *get_unlocked_entry(struct xa_state *xas) +static void *get_unlocked_entry(struct xa_state *xas, unsigned int order) { void *entry; struct wait_exceptional_entry_queue ewait; @@ -210,6 +221,8 @@ static void *get_unlocked_entry(struct x for (;;) { entry = xas_find_conflict(xas); + if (dax_entry_order(entry) < order) + return XA_RETRY_ENTRY; if (!entry || WARN_ON_ONCE(!xa_is_value(entry)) || !dax_is_locked(entry)) return entry; @@ -254,7 +267,7 @@ static void wait_entry_unlocked(struct x static void put_unlocked_entry(struct xa_state *xas, void *entry) { /* If we were the only waiter woken, wake the next one */ - if (entry) + if (entry && dax_is_conflict(entry)) dax_wake_entry(xas, entry, false); } @@ -461,7 +474,7 @@ void dax_unlock_page(struct page *page, * overlap with xarray value entries. */ static void *grab_mapping_entry(struct xa_state *xas, - struct address_space *mapping, unsigned long size_flag) + struct address_space *mapping, unsigned int order) { unsigned long index = xas->xa_index; bool pmd_downgrade = false; /* splitting PMD entry into PTE entries? */ @@ -469,20 +482,17 @@ static void *grab_mapping_entry(struct x retry: xas_lock_irq(xas); - entry = get_unlocked_entry(xas); + entry = get_unlocked_entry(xas, order); if (entry) { + if (dax_is_conflict(entry)) + goto fallback; if (!xa_is_value(entry)) { xas_set_err(xas, EIO); goto out_unlock; } - if (size_flag & DAX_PMD) { - if (dax_is_pte_entry(entry)) { - put_unlocked_entry(xas, entry); - goto fallback; - } - } else { /* trying to grab a PTE entry */ + if (order == 0) { if (dax_is_pmd_entry(entry) && (dax_is_zero_entry(entry) || dax_is_empty_entry(entry))) { @@ -523,7 +533,11 @@ retry: if (entry) { dax_lock_entry(xas, entry); } else { - entry = dax_make_entry(pfn_to_pfn_t(0), size_flag | DAX_EMPTY); + unsigned long flags = DAX_EMPTY; + + if (order > 0) + flags |= DAX_PMD; + entry = dax_make_entry(pfn_to_pfn_t(0), flags); dax_lock_entry(xas, entry); if (xas_error(xas)) goto out_unlock; @@ -594,7 +608,7 @@ struct page *dax_layout_busy_page(struct if (WARN_ON_ONCE(!xa_is_value(entry))) continue; if (unlikely(dax_is_locked(entry))) - entry = get_unlocked_entry(&xas); + entry = get_unlocked_entry(&xas, 0); if (entry) page = dax_busy_page(entry); put_unlocked_entry(&xas, entry); @@ -621,7 +635,7 @@ static int __dax_invalidate_entry(struct void *entry; xas_lock_irq(&xas); - entry = get_unlocked_entry(&xas); + entry = get_unlocked_entry(&xas, 0); if (!entry || WARN_ON_ONCE(!xa_is_value(entry))) goto out; if (!trunc && @@ -848,7 +862,7 @@ static int dax_writeback_one(struct xa_s if (unlikely(dax_is_locked(entry))) { void *old_entry = entry; - entry = get_unlocked_entry(xas); + entry = get_unlocked_entry(xas, 0); /* Entry got punched out / reallocated? */ if (!entry || WARN_ON_ONCE(!xa_is_value(entry))) @@ -1509,7 +1523,7 @@ static vm_fault_t dax_iomap_pmd_fault(st * entry is already in the array, for instance), it will return * VM_FAULT_FALLBACK. */ - entry = grab_mapping_entry(&xas, mapping, DAX_PMD); + entry = grab_mapping_entry(&xas, mapping, PMD_ORDER); if (xa_is_internal(entry)) { result = xa_to_internal(entry); goto fallback; @@ -1658,11 +1672,10 @@ dax_insert_pfn_mkwrite(struct vm_fault * vm_fault_t ret; xas_lock_irq(&xas); - entry = get_unlocked_entry(&xas); + entry = get_unlocked_entry(&xas, order); /* Did we race with someone splitting entry or so? */ - if (!entry || - (order == 0 && !dax_is_pte_entry(entry)) || - (order == PMD_ORDER && !dax_is_pmd_entry(entry))) { + if (!entry || dax_is_conflict(entry) || + (order == 0 && !dax_is_pte_entry(entry))) { put_unlocked_entry(&xas, entry); xas_unlock_irq(&xas); trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,