linux-kernel - Re: [PATCH v3 15/38] x86/resctrl: Move monitor exit work to a restrl exit call

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Date: Fri, 28 Jun 2024 09:46:56 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, H Peter Anvin
	<hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	<shameerali.kolothum.thodi@...wei.com>, D Scott Phillips OS
	<scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
	<tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
	"Dave Martin" <dave.martin@....com>, Shaopeng Tan
	<tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v3 15/38] x86/resctrl: Move monitor exit work to a restrl
 exit call

Hi James,

On 6/14/24 8:00 AM, James Morse wrote:
> rdt_put_mon_l3_config() is called via the architecture's
> resctrl_arch_exit() call, and appears to free the rmid_ptrs[]
> and closid_num_dirty_rmid[] arrays. In reality this code is marked
> __exit, and is removed by the linker as resctl can't be built
> as a module.
> 
> To separate the filesystem and architecture parts of resctrl,
> this free()ing work needs to be triggered by the filesystem,
> as these structures belong to the filesystem code.
> 
> Rename rdt_put_mon_l3_config() resctrl_mon_resource_exit()
> and call it from resctrl_exit(). The kfree() is currently
> dependent on r->mon_capable. resctrl_mon_resource_init()

resctrl_mon_resource_init() does not exist at this point making
this motivation difficult to follow.

> takes no arguments, so resctrl_mon_resource_exit() shouldn't
> take any either. Add the check to dom_data_exit(), making it
> take the resource as an argument. This makes it more symmetrical
> with dom_data_init().
> 
> Signed-off-by: James Morse <james.morse@....com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> ---
> Changes since v2:
>   * Dropped __exit as needed in the next patch.
> 
> Change since v1:
>   * [Commit message only] Typo fixes:
>     s/restrl/resctrl/g
>     s/resctl/resctrl/g

Something went wrong here since the subject and changelog still contains
the terms that were intended to be replaced.

> 
>   * [Commit message only] Reword second paragraph to remove reference to
>     the MPAM error interrupt, which provides background rationale for a
>     later patch rather than for this patch, and so it is not really
>     relevant here.
> ---
>   arch/x86/kernel/cpu/resctrl/core.c     |  5 -----
>   arch/x86/kernel/cpu/resctrl/internal.h |  2 +-
>   arch/x86/kernel/cpu/resctrl/monitor.c  | 12 ++++++++----
>   arch/x86/kernel/cpu/resctrl/rdtgroup.c |  2 ++
>   4 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 9ad660b2b097..2540a7cb11b0 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -950,14 +950,9 @@ late_initcall(resctrl_arch_late_init);
>   
>   static void __exit resctrl_arch_exit(void)
>   {
> -	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> -
>   	cpuhp_remove_state(rdt_online);
>   
>   	resctrl_exit();
> -
> -	if (r->mon_capable)
> -		rdt_put_mon_l3_config();
>   }
>   
>   __exitcall(resctrl_arch_exit);
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 7ede340b1301..9aa7f587484c 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -535,7 +535,7 @@ void closid_free(int closid);
>   int alloc_rmid(u32 closid);
>   void free_rmid(u32 closid, u32 rmid);
>   int rdt_get_mon_l3_config(struct rdt_resource *r);
> -void __exit rdt_put_mon_l3_config(void);
> +void resctrl_mon_resource_exit(void);
>   bool __init rdt_cpu_has(int flag);
>   void mon_event_count(void *info);
>   int rdtgroup_mondata_show(struct seq_file *m, void *arg);
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 3e5375c365e6..7d6aebce75c1 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -965,10 +965,12 @@ static int dom_data_init(struct rdt_resource *r)
>   	return err;
>   }
>   
> -static void __exit dom_data_exit(void)
> +static void dom_data_exit(struct rdt_resource *r)
>   {
> -	mutex_lock(&rdtgroup_mutex);
> +	if (!r->mon_capable)
> +		return;
>   
> +	mutex_lock(&rdtgroup_mutex);

I know there has been a bit of back&forth on whether the mutex is needed
here. With this change moving dom_data_exit() out from __exit I think
the locking should aim to be consistent with existing runtime
and thus the check of r->mon_capable should be with mutex held. Having
this little snippet outside mutex will just cause confusion. Do you
have motivation for needing this be done outside of mutex? I think it
ended up this way with this patch aiming to keep existing flow exactly,
but that ended up as convenience in a flow where mutex was not really
needed at all.

Reinette