Re: [PATCH] hazptr: handle NULL address in hazptr_detach

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2026-09-08 12:22, Paul E. McKenney wrote:
> On Tue, Sep 08, 2026 at 11:29:31AM -0400, Mathieu Desnoyers wrote:
>> On 2026-09-08 11:24, Bradley Morgan wrote:
>>> On 8 September 2026 16:22:14 BST, Mathieu Desnoyers
>>> <mathieu.desnoyers@efficios.com> wrote:
>>>> When hazptr_acquire loads a NULL pointer, it sets:
>>>>
>>>> - slot_item->slot.addr = NULL,
>>>> - slot_item->ctx.ctx = ctx
>>>> - ctx->slot = slot
>>>>
>>>> And it returns NULL.
>>>>
>>>> Then hazptr_detach is called on this ctx, it will act on the ctx as if
>>>> needed to be promoted to backup slot, even though it has a NULL addr.
>>>>
>>>> Looking at what hazptr_note_context_switch() does before promoting
>>>> to backup slot, it checks for a NULL slot->addr, which is exactly
>>>> what is missing from hazptr_detach.
>>>>
>>>> With this in place there would be no need to explicitly check the
>>>> hazptr_acquire() return value before calling hazptr_detach().
>>>>
>>>> hazptr_release() has a early return check for NULL addr as well, so it
>>>> makes sense that detach does an early return (no-op) similarly.
>>>>
>>>
>>> You shall kill me for this!!
>>>
>>> Could you perhaps do a splat in ze commit description pls?
>>
>> The splat is available at the "Closes" URL below. I'm not sure whether
>> we should duplicate this verbose information ?
>>
>> Paul ?
> 
> I am fine either way, as long as the information is reasonably easily
> accessible.  Which is the case either way.  ;-)

Then I favor a concise commit message, leaving the splat details to the
"Closes" link. Feel free to pick up this patch for testing.

Thank you!

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com