[rh7,09/14] root dentries need RCU-delayed freeing

Submitted by Andrey Ryabinin on June 10, 2019, 3:13 p.m.

Details

Message ID 20190610151400.12820-9-aryabinin@virtuozzo.com
State New
Series "Series without cover letter"
Headers show

Commit Message

Andrey Ryabinin June 10, 2019, 3:13 p.m.
From: Al Viro <viro@zeniv.linux.org.uk>

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 <viro@zeniv.linux.org.uk>
(cherry picked from commit 90bad5e05bcdb0308cfa3d3a60f5c0b9c8e2efb3)
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 fs/dcache.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Patch hide | download patch | download mbox

diff --git a/fs/dcache.c b/fs/dcache.c
index d01631c62ddb..e24229628475 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1883,10 +1883,12 @@  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;
 }