tree 86b13e3566df266dffd4c18610d68bde4e90b5e3
parent 9e1ff307c779ce1f0f810c7ecce3d95bbae40896
author Ian Kent <raven@themaw.net> 1633309433 +0800
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1633336038 +0200

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 <yi.zhang@redhat.com>
ACKed-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/163330943316.19450.15056895533949392922.stgit@mickey.themaw.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>