Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932427AbcKGNF7 (ORCPT ); Mon, 7 Nov 2016 08:05:59 -0500 Received: from mx2.suse.de ([195.135.220.15]:36939 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932369AbcKGNFq (ORCPT ); Mon, 7 Nov 2016 08:05:46 -0500 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Oleg Nesterov , Al Viro , Jiri Slaby Subject: [PATCH 3.12 45/72] fs/super.c: fix race between freeze_super() and thaw_super() Date: Mon, 7 Nov 2016 14:04:52 +0100 Message-Id: X-Mailer: git-send-email 2.10.2 In-Reply-To: <0f3caac741164dcff670ae0f4d1cfcb0a7026a1c.1478523828.git.jslaby@suse.cz> References: <0f3caac741164dcff670ae0f4d1cfcb0a7026a1c.1478523828.git.jslaby@suse.cz> In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1757 Lines: 51 From: Oleg Nesterov 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit 89f39af129382a40d7cd1f6914617282cfeee28e upstream. Change thaw_super() to check frozen != SB_FREEZE_COMPLETE rather than frozen == SB_UNFROZEN, otherwise it can race with freeze_super() which drops sb->s_umount after SB_FREEZE_WRITE to preserve the lock ordering. In this case thaw_super() will wrongly call s_op->unfreeze_fs() before it was actually frozen, and call sb_freeze_unlock() which leads to the unbalanced percpu_up_write(). Unfortunately lockdep can't detect this, so this triggers misc BUG_ON()'s in kernel/rcu/sync.c. Reported-and-tested-by: Nikolay Borisov Signed-off-by: Oleg Nesterov Signed-off-by: Al Viro Signed-off-by: Jiri Slaby --- fs/super.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/super.c b/fs/super.c index e3406833d82f..d9a7d620e747 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1337,8 +1337,8 @@ int freeze_super(struct super_block *sb) } } /* - * This is just for debugging purposes so that fs can warn if it - * sees write activity when frozen is set to SB_FREEZE_COMPLETE. + * For debugging purposes so that fs can warn if it sees write activity + * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super(). */ sb->s_writers.frozen = SB_FREEZE_COMPLETE; up_write(&sb->s_umount); @@ -1357,7 +1357,7 @@ int thaw_super(struct super_block *sb) int error; down_write(&sb->s_umount); - if (sb->s_writers.frozen == SB_UNFROZEN) { + if (sb->s_writers.frozen != SB_FREEZE_COMPLETE) { up_write(&sb->s_umount); return -EINVAL; } -- 2.10.2