Re: [PATCH 1/3] rcu: Return early if callback is not specified

[Uladzislau Rezki <urezki@gmail.com>]

On Thu, Jun 12, 2025 at 10:30:38AM -0700, Boqun Feng wrote:
> 
> 
> On Tue, Jun 10, 2025, at 12:33 PM, Joel Fernandes wrote:
> > On 6/10/2025 1:34 PM, Uladzislau Rezki (Sony) wrote:
> >> Currently the call_rcu() API does not check whether a callback
> >> pointer is NULL. If NULL is passed, rcu_core() will try to invoke
> >> it, resulting in NULL pointer dereference and a kernel crash.
> >> 
> >> To prevent this and improve debuggability, this patch adds a check
> >> for NULL and emits a kernel stack trace to help identify a faulty
> >> caller.
> >> 
> >> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> >
> > Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
> >
> 
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> 
Thank you for review, Boqun!

> > I will add this first one (only this one since we're discussing the others) to a
> > new rcu/fixes-for-6.16 branch, but let me know if any objections.
> >
> 
> Not sure it’s urgent enough given the current evidence.
> 
Let me clarify it a bit. My point is that, we get a kernel crash in a
subsystem we are responsible for, i.e. no matter if there are faulty
users of it(third party applications), the point is users can crash it.

The kernel robot reports it and it is already a strong indication that
the subsystem is not hardened against invalid inputs:

"BUG: unable to handle kernel NULL pointer dereference in rcu_core (3)"

so this in the rcu_core() which is part of RCU.

But, anyway Joel should decide. I shared my opinion :)

--
Uladzislau Rezki