From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754422AbdBETw3 (ORCPT + 2 others); Sun, 5 Feb 2017 14:52:29 -0500 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:28194 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754137AbdBETZ6 (ORCPT ); Sun, 5 Feb 2017 14:25:58 -0500 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: Oleg Nesterov , Al Viro , Willy Tarreau Subject: [PATCH 3.10 174/319] fs/super.c: fix race between freeze_super() and thaw_super() Date: Sun, 5 Feb 2017 20:19:56 +0100 Message-Id: <1486322541-8206-75-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1486322541-8206-1-git-send-email-w@1wt.eu> References: <1486322541-8206-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 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: Willy Tarreau --- fs/super.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/super.c b/fs/super.c index 97280e7..fd3281d 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1327,8 +1327,8 @@ 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); @@ -1347,7 +1347,7 @@ 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; } -- 2.8.0.rc2.1.gbe9624a