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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham 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 3E7A3C76191 for ; Thu, 25 Jul 2019 08:27:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0467021871 for ; Thu, 25 Jul 2019 08:27:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389631AbfGYI1c (ORCPT ); Thu, 25 Jul 2019 04:27:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:58908 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2389624AbfGYI1c (ORCPT ); Thu, 25 Jul 2019 04:27:32 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 8F037AFBE for ; Thu, 25 Jul 2019 08:27:31 +0000 (UTC) From: Nikolay Borisov To: linux-btrfs@vger.kernel.org Cc: Nikolay Borisov Subject: [PATCH 2/2] btrfs: Fix deadlock caused by missing memory barrier Date: Thu, 25 Jul 2019 11:27:29 +0300 Message-Id: <20190725082729.14109-3-nborisov@suse.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190725082729.14109-1-nborisov@suse.com> References: <20190725082729.14109-1-nborisov@suse.com> Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Commit 06297d8cefca ("btrfs: switch extent_buffer blocking_writers from atomic to int") changed the type of blocking_writers but forgot to adjust relevant code in btrfs_tree_unlock by converting the smp_mb__after_atomic to smp_mb. This opened up the possibility of a deadlock due to re-ordering of setting blocking_writers and checking/waking up the waiter. This particular lockup is explained in a comment above waitqueue_active() function. Fix it by converting the memory barrier to a full smp_mb, accounting for the fact that blocking_writers is a simple integer. Fixes: 06297d8cefca ("btrfs: switch extent_buffer blocking_writers from atomic to int") Signed-off-by: Nikolay Borisov Tested-by: Johannes Thumshirn --- fs/btrfs/locking.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index ceb23690b89b..5e867720df88 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -310,9 +310,12 @@ void btrfs_tree_unlock(struct extent_buffer *eb) if (blockers) { btrfs_assert_no_spinning_writers(eb); eb->blocking_writers--; - /* Use the lighter barrier after atomic */ - smp_mb__after_atomic(); - cond_wake_up_nomb(&eb->write_lock_wq); + /* + * We need to order modifying blocking_writers above with + * actually waking up the sleepers to ensure they see the + * updated value of blocking_writers + */ + cond_wake_up(&eb->write_lock_wq); } else { btrfs_assert_spinning_writers_put(eb); write_unlock(&eb->lock); -- 2.17.1