Re: [PATCH v10 RESEND 02/15] fs/resctrl: Skip monitor context allocation when force-freeing RMIDs

[Jinjie Ruan]

Hi Reinette,

在 2026/10/29 5:29, Reinette Chatre 写道:
> Hi Jinjie,
> 
> On 10/26/26 6:33 PM, Jinjie Ruan wrote:
>>
>>
>> 在 2026/10/26 22:11, Ben Horgan 写道:
>>> Hi Jinjie,
>>>
>>> On 26/10/2026 14:08, Ben Horgan wrote:
>>>> Hi Jinjie,
>>>>
>>>> On 20/10/2026 14:42, Jinjie Ruan wrote:
>>>>> __check_limbo() allocates the architecture monitor context before the
>>>>> scan loop, even when force_free is set. The force-free path never reads
>>>>> occupancy and never uses the context.
>>>>>
>>>>> If the allocation fails, the function returns early and leaves the limbo
>>>>> list unflushed. Callers such as the unmount path then silently fail to
>>>>> return the RMIDs to the free list, leaving stale CLOSIDs in limbo that
>>>>> are re-interpreted with the CDP state of the next mount.
>>>>
>>>> Is this a theoretical fix or is there some way that resctrl_arch_mon_ctx_alloc() can fail in practice?
>>>
>>> This does seem a good change to me and we do have to consider that the memory alocation might fail.
>>
>> Hi Ben,
>>
>> I agree. force_free=true not rely on the allocation of arch_mon_ctx
>> succeeding, we should directly loop to free the RMID.
>>
>> Perhaps a small refactor is needed to split __check_limbo() into two
>> versions as there isn't much duplication?
> I agree that a split would look better here. With these additional checks of
> force_free the __check_limbo() is becoming hard to follow. Even more than

I agree.

> two versions of __check_limbo() this could just be two distinct functions,
> for example a new "void release_limbo_rmids(struct rdt_l3_mon_domain *d)"
> that is only called from resctrl_offline_l3_mon_domain().

Thank you! will adopt this naming.

> 
> The changelog mentions the unmount path but it seems that the issue is with
> domains going offline instead? As far as I understand the limbo state is not
> impacted by mount/unmount.

You're right, I misunderstood — it's when the domain goes offline.

> 
> I also think that the "Fixes:" tag should instead be:
> 	fc16126cc11d ("x86,fs/resctrl: Prevent out-of-bounds access while offlining CPU when SNC enabled")

Thank you! I got it.

> 
> The first two fixes in this series look appropriate for resctrl fs. I'd like
> to echo Ben's request to submit them separately from this work.

Thank you! I will send it separately shortly.

> 
> Thank you very much.
> 
> Reinette

-- 
Best regards,
Jinjie