From patchwork Thu Jan 2 22:07:00 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 234718 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=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, 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 1E94CC3276E for ; Thu, 2 Jan 2020 22:30:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E4A9A2253D for ; Thu, 2 Jan 2020 22:30:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578004227; bh=m5jp6toHKvY6DICKeFo4tapw/949r6gZ/yCWEKg4VJw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=szoC9sYCbmJyhamRxlMApLLezbAhg2U3HqUIbttmd1iSamaQlerb59tz8h8wkUCN5 33yCfmEE4GmTcFwHay+2x/z8gJ9+PEMfA0e2WRUQWWSBBT7D3wMOLIMELKbPk3M2Pq kQIbXyPdpqhv+QsPLtTGF7HBpv3vZsJMxKO+afVI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729903AbgABWaZ (ORCPT ); Thu, 2 Jan 2020 17:30:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:34168 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729899AbgABWaZ (ORCPT ); Thu, 2 Jan 2020 17:30:25 -0500 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 E9EA220863; Thu, 2 Jan 2020 22:30:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578004224; bh=m5jp6toHKvY6DICKeFo4tapw/949r6gZ/yCWEKg4VJw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=2bQ3BXDR4LWA2BFtmzyfuTqnhUDfBgVUjkMR9v9o6vMARSO2zWCakPA4mrFqx62NT SPjGtwlXbNF9Xk3eFyddst0kFe3zYO11usjSfyC0hpcaRHB8Wta/93ePuI9YGNMNfd i4w7UmakKt1WPqY8iBM9FnCxcMw1OuS/XMnHQ3J0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josef Bacik , David Sterba , Sasha Levin Subject: [PATCH 4.9 089/171] btrfs: do not call synchronize_srcu() in inode_tree_del Date: Thu, 2 Jan 2020 23:07:00 +0100 Message-Id: <20200102220559.438935083@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200102220546.960200039@linuxfoundation.org> References: <20200102220546.960200039@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Josef Bacik [ Upstream commit f72ff01df9cf5db25c76674cac16605992d15467 ] Testing with the new fsstress uncovered a pretty nasty deadlock with lookup and snapshot deletion. Process A unlink -> final iput -> inode_tree_del -> synchronize_srcu(subvol_srcu) Process B btrfs_lookup <- srcu_read_lock() acquired here -> btrfs_iget -> find inode that has I_FREEING set -> __wait_on_freeing_inode() We're holding the srcu_read_lock() while doing the iget in order to make sure our fs root doesn't go away, and then we are waiting for the inode to finish freeing. However because the free'ing process is doing a synchronize_srcu() we deadlock. Fix this by dropping the synchronize_srcu() in inode_tree_del(). We don't need people to stop accessing the fs root at this point, we're only adding our empty root to the dead roots list. A larger much more invasive fix is forthcoming to address how we deal with fs roots, but this fixes the immediate problem. Fixes: 76dda93c6ae2 ("Btrfs: add snapshot/subvolume destroy ioctl") CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/inode.c | 1 - 1 file changed, 1 deletion(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index bb8863958ac0..250c8403ec67 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5576,7 +5576,6 @@ static void inode_tree_del(struct inode *inode) spin_unlock(&root->inode_lock); if (empty && btrfs_root_refs(&root->root_item) == 0) { - synchronize_srcu(&root->fs_info->subvol_srcu); spin_lock(&root->inode_lock); empty = RB_EMPTY_ROOT(&root->inode_tree); spin_unlock(&root->inode_lock);