Re: [BUG, PATCH 03/10] sysfs: added __compat_only_sysfs_link_entry_to_kobj()

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Fri, Nov 06, 2015 at 06:55:18PM -0800, Jeremiah Mahler wrote:
> Jarkko,
> 
> On Fri, Oct 16, 2015 at 09:40:22PM +0300, Jarkko Sakkinen wrote:
> > Added a new function __compat_only_sysfs_link_group_to_kobj() that adds
> > a symlink from attribute or group to a kobject. This needed for
> > maintaining backwards compatibility with PPI attributes in the TPM
> > driver.
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> > ---
> >  fs/sysfs/group.c      | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/sysfs.h | 11 +++++++++++
> >  2 files changed, 55 insertions(+)
> > 
> > diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
> > index 39a0199..e123659 100644
> > --- a/fs/sysfs/group.c
> > +++ b/fs/sysfs/group.c
> > @@ -352,3 +352,47 @@ void sysfs_remove_link_from_group(struct kobject *kobj, const char *group_name,
> >  	}
> >  }
> >  EXPORT_SYMBOL_GPL(sysfs_remove_link_from_group);
> > +
> > +/**
> > + * __compat_only_sysfs_link_entry_to_kobj - add a symlink to a kobject pointing
> > + * to a group or an attribute
> > + * @kobj:		The kobject containing the group.
> > + * @target_kobj:	The target kobject.
> > + * @target_name:	The name of the target group or attribute.
> > + */
> > +int __compat_only_sysfs_link_entry_to_kobj(struct kobject *kobj,
> > +				      struct kobject *target_kobj,
> > +				      const char *target_name)
> > +{
> > +	struct kernfs_node *target;
> > +	struct kernfs_node *entry;
> > +	struct kernfs_node *link;
> > +
> > +	/*
> > +	 * We don't own @target_kobj and it may be removed at any time.
> > +	 * Synchronize using sysfs_symlink_target_lock. See sysfs_remove_dir()
> > +	 * for details.
> > +	 */
> > +	spin_lock(&sysfs_symlink_target_lock);
> > +	target = target_kobj->sd;
> > +	if (target)
> > +		kernfs_get(target);
> > +	spin_unlock(&sysfs_symlink_target_lock);
> > +	if (!target)
> > +		return -ENOENT;
> > +
> > +	entry = kernfs_find_and_get(target_kobj->sd, target_name);
> > +	if (!entry) {
> > +		kernfs_put(target);
> > +		return -ENOENT;
> > +	}
> > +
> 
> On an Acer C720 this call to kernfs_find_and_get fails resulting in
> a failed resume after suspend.
> 
> Apparently it can't find an object for the name "ppi".
> 
> This bug does not appear until the next patch is applied which
> calls __compat_only_sysfs_link_entry_to_kobj.

I think I might have found something thanks to your help

First I found this old bug:

https://bugzilla.redhat.com/show_bug.cgi?id=1096511

What is happening is that DSM is not found and therefore tpm_add_ppi()
does not add ppi to sysfs groups array.

__compat_only_sysfs_link_entry_to_kobj() is called after tpm_add_ppi
unconditionally for TPM1.

I'll implement a fix for this ASAP.

Thank you for great effort on finding tis!

> -- 
> - Jeremiah Mahler

/Jarkko