Re: [RFC PATCH 0/4] Add hazard pointers to kernel

[Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>]

On 9/19/2024 12:16 PM, Linus Torvalds wrote:
> On Thu, 19 Sept 2024 at 00:44, Neeraj Upadhyay <Neeraj.Upadhyay@amd.com> wrote:
>>
>> While we were working on this problem, this refcount scalability issue got
>> resolved  recently with conditional ref acquisition [3] (however, there are new
>> developments in apparmor code which might bring back the refcount problem [4]).
> 
> Honestly, the various security layers should be a whole lot more
> careful about their horrid performance issues, and I think that [4]
> you point at needs to just be headed off at the pass.
> 
> No  more "the security layer is so bad at performance that we have to
> introduce new ref mechanisms", please. Let's push back on bad security
> layer code instead.
> 

Ok got it. Thanks for your feedback! I had tried using percpu refcount first
(in place of kref) in AppArmor. However, that required managing the last
reference drop (implemented in [1] and [2]). Mateusz has shared some ideas
in his reply to this thread. Maybe that is a workable solution. Will defer
to John on this as I have limited understanding of the cred management code.


- Neeraj

>                 Linus