Re: [REPOST,UPDATED PATCH] kernfs: don't create a negative dentry if inactive node exists

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Oct 04, 2021 at 01:07:46AM +0000, Al Viro wrote:
> On Mon, Oct 04, 2021 at 09:03:53AM +0800, Ian Kent wrote:
> > 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.
> 
> Looks sane, but which tree should it go through?  I can pick it, but I've
> no idea if anybody already has kernfs work in their trees...

I can take it, kernfs patches normally go through my tree, can I get an
acked-by?

thanks,

greg k-h