From aa60dca6b21c8328221d824e643b8fe00089d69c Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 6 Aug 2018 09:03:58 -0400 Subject: [PATCH] root dentries need RCU-delayed freeing 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") Signed-off-by: Al Viro Signed-off-by: Ben Hutchings --- fs/dcache.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 7befa3a373cf..2b4f8d2d1347 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1812,10 +1812,12 @@ struct dentry *d_make_root(struct inode *root_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; } -- 2.34.1