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=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 E91DCC3276C for ; Thu, 2 Jan 2020 22:41:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AF85F217F4 for ; Thu, 2 Jan 2020 22:41:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578004914; bh=kl004tIylIy2HeVOharYYJ5vMSraklAz5CHA3QF/Qis=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=uHxrflRD3Axp7/vvQihGR6QHjVEdvtmb6/xMD/btypP0T9bIYc8bWPfEsubJRVc7P 66PoizdGwLKO8YZmNUq+2q0m9Vnb8UwDIrb7ADnWEneJ96hp7S2RZMRuVd7VhnL5Z7 QYCSL/YqBpFK5AgFvpI9J9kkodE6RzO9S2BpUZvM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730971AbgABWgi (ORCPT ); Thu, 2 Jan 2020 17:36:38 -0500 Received: from mail.kernel.org ([198.145.29.99]:47510 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730940AbgABWgY (ORCPT ); Thu, 2 Jan 2020 17:36:24 -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 163AE21D7D; Thu, 2 Jan 2020 22:36:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578004583; bh=kl004tIylIy2HeVOharYYJ5vMSraklAz5CHA3QF/Qis=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=aUQ8TfKBAfEPidlHDPd/GxO/lGECgfvBaDWIuaV7C8f61VTcj5zQZG/Wh7lwQaejS SO0WpCdjkG6P/bDNLCUKCxByEsKp643zzqW62dzBhnnGlcfmJyLdQZ/EOlr8LBm830 xi7PPlNJK4OAKmyst7yGJzKOXfNuVgH78/52pQkE= 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 4.4 068/137] btrfs: do not call synchronize_srcu() in inode_tree_del Date: Thu, 2 Jan 2020 23:07:21 +0100 Message-Id: <20200102220555.698776544@linuxfoundation.org> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200102220546.618583146@linuxfoundation.org> References: <20200102220546.618583146@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 383717ccecc7..548e9cd1a337 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5506,7 +5506,6 @@ 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); -- 2.20.1