Re: [PATCH v2 12/17] xen/hypfs: add new enter() and exit() per node callbacks

[Jan Beulich <jbeulich@suse.com>]

On 03.12.2020 16:14, Jürgen Groß wrote:
> On 03.12.20 15:59, Jan Beulich wrote:
>> On 01.12.2020 09:21, Juergen Gross wrote:
>>> @@ -100,11 +112,58 @@ static void hypfs_unlock(void)
>>>       }
>>>   }
>>>   
>>> +const struct hypfs_entry *hypfs_node_enter(const struct hypfs_entry *entry)
>>> +{
>>> +    return entry;
>>> +}
>>> +
>>> +void hypfs_node_exit(const struct hypfs_entry *entry)
>>> +{
>>> +}
>>> +
>>> +static int node_enter(const struct hypfs_entry *entry)
>>> +{
>>> +    const struct hypfs_entry **last = &this_cpu(hypfs_last_node_entered);
>>> +
>>> +    entry = entry->funcs->enter(entry);
>>> +    if ( IS_ERR(entry) )
>>> +        return PTR_ERR(entry);
>>> +
>>> +    ASSERT(!*last || *last == entry->parent);
>>> +
>>> +    *last = entry;
>>> +
>>> +    return 0;
>>> +}
>>> +
>>> +static void node_exit(const struct hypfs_entry *entry)
>>> +{
>>> +    const struct hypfs_entry **last = &this_cpu(hypfs_last_node_entered);
>>> +
>>> +    if ( !*last )
>>> +        return;
>>
>> Under what conditions is this legitimate to happen? IOW shouldn't
>> there be an ASSERT_UNREACHABLE() here?
> 
> This is for the "/" node.

I.e. would ASSERT(!entry->parent) be appropriate to add here, at
the same time serving as documentation of what you've just said?

Jan