From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:48816 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753655AbcJZIoS (ORCPT ); Wed, 26 Oct 2016 04:44:18 -0400 Subject: Patch "fs/super.c: fix race between freeze_super() and thaw_super()" has been added to the 4.8-stable tree To: oleg@redhat.com, gregkh@linuxfoundation.org, kernel@kyup.com, viro@zeniv.linux.org.uk Cc: , From: Date: Wed, 26 Oct 2016 10:44:23 +0200 Message-ID: <1477471463147158@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled fs/super.c: fix race between freeze_super() and thaw_super() to the 4.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: fs-super.c-fix-race-between-freeze_super-and-thaw_super.patch and it can be found in the queue-4.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 89f39af129382a40d7cd1f6914617282cfeee28e Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 26 Sep 2016 18:07:48 +0200 Subject: fs/super.c: fix race between freeze_super() and thaw_super() From: Oleg Nesterov 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: Greg Kroah-Hartman --- fs/super.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/fs/super.c +++ b/fs/super.c @@ -1379,8 +1379,8 @@ 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); @@ -1399,7 +1399,7 @@ 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; } Patches currently in stable-queue which might be from oleg@redhat.com are queue-4.8/fs-super.c-fix-race-between-freeze_super-and-thaw_super.patch