From 410d591a19543f1347bc2b4b4ec3399cb548ba47 Mon Sep 17 00:00:00 2001 From: Ian Kent Date: Mon, 4 Oct 2021 09:03:53 +0800 Subject: kernfs: don't create a negative dentry if inactive node exists It's been reported that doing stress test for module insertion and removal can result in an ENOENT from libkmod for a valid module. In kernfs_iop_lookup() a negative dentry is created if there's no kernfs node associated with the dentry or the node is inactive. But inactive kernfs nodes are meant to be invisible to the VFS and creating a negative dentry for these can have unexpected side effects when the node transitions to an active state. The point of creating negative dentries is to avoid the expensive alloc/free cycle that occurs if there are frequent lookups for kernfs attributes that don't exist. So kernfs nodes that are not yet active should not result in a negative dentry being created so when they transition to an active state VFS lookups can create an associated dentry is a natural way. It's also been reported that https://github.com/osandov/blktests.git test block/001 hangs during the test. It was suggested that recent changes to blktests might have caused it but applying this patch resolved the problem without change to blktests. Fixes: c7e7c04274b1 ("kernfs: use VFS negative dentry caching") Tested-by: Yi Zhang ACKed-by: Al Viro Signed-off-by: Ian Kent Link: https://lore.kernel.org/r/163330943316.19450.15056895533949392922.stgit@mickey.themaw.net Signed-off-by: Greg Kroah-Hartman --- fs/kernfs/dir.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index cfc3ce8b815a..8e0a1378a4b1 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1111,7 +1111,14 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir, kn = kernfs_find_ns(parent, dentry->d_name.name, ns); /* attach dentry and inode */ - if (kn && kernfs_active(kn)) { + if (kn) { + /* Inactive nodes are invisible to the VFS so don't + * create a negative. + */ + if (!kernfs_active(kn)) { + up_read(&kernfs_rwsem); + return NULL; + } inode = kernfs_get_inode(dir->i_sb, kn); if (!inode) inode = ERR_PTR(-ENOMEM); -- cgit v1.2.3