From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Al Viro Subject: [PATCH 3.18 02/15] root dentries need RCU-delayed freeing Date: Thu, 16 Aug 2018 20:41:39 +0200 Message-Id: <20180816171633.637791038@linuxfoundation.org> In-Reply-To: <20180816171633.546734046@linuxfoundation.org> References: <20180816171633.546734046@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro commit 90bad5e05bcdb0308cfa3d3a60f5c0b9c8e2efb3 upstream. Since mountpoint crossing can happen without leaving lazy mode, root dentries do need the same protection against having their memory freed without RCU delay as everything else in the tree. It's partially hidden by RCU delay between detaching from the mount tree and dropping the vfsmount reference, but the starting point of pathwalk can be on an already detached mount, in which case umount-caused RCU delay has already passed by the time the lazy pathwalk grabs rcu_read_lock(). If the starting point happens to be at the root of that vfsmount *and* that vfsmount covers the entire filesystem, we get trouble. Fixes: 48a066e72d97 ("RCU'd vsfmounts") Cc: stable@vger.kernel.org Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- fs/dcache.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1848,10 +1848,12 @@ struct dentry *d_make_root(struct inode static const struct qstr name = QSTR_INIT("/", 1); res = __d_alloc(root_inode->i_sb, &name); - if (res) + if (res) { + res->d_flags |= DCACHE_RCUACCESS; d_instantiate(res, root_inode); - else + } else { iput(root_inode); + } } return res; }