Re: [PATCH v7 16/24] x86/resctrl: Make resctrl_mounted checks explicit

[Moger, Babu]

On 10/25/23 13:03, James Morse wrote:
> The rdt_enable_key is switched when resctrl is mounted, and used to
> prevent a second mount of the filesystem. It also enables the
> architecture's context switch code.
> 
> This requires another architecture to have the same set of static-keys,
> as resctrl depends on them too. The existing users of these static-keys
> are implicitly also checking if the filesystem is mounted.
> 
> Make the resctrl_mounted checks explicit: resctrl can keep track of
> whether it has been mounted once. This doesn't need to be combined with
> whether the arch code is context switching the CLOSID.
> 
> rdt_mon_enable_key is never used just to test that resctrl is mounted,
> but does also have this implication. Add a resctrl_mounted to all uses
> of rdt_mon_enable_key. This will allow rdt_mon_enable_key to be swapped
> with a helper in a subsequent patch.
> 
> This will allow the static-key changing to be moved behind resctrl_arch_
> calls.
> 
> Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
> Tested-by: Peter Newman <peternewman@xxxxxxxxxx>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
> Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>

Reviewed-by: Babu Moger <babu.moger@xxxxxxx>
> 
> ---
> Changes since v3:
>  * Removed a newline.
>  * Rephrased commit message
> 
> Changes since v4:
>  * Rephrased comment.
> 
> No changes since v6
> ---
>  arch/x86/kernel/cpu/resctrl/internal.h |  1 +
>  arch/x86/kernel/cpu/resctrl/monitor.c  | 12 ++++++++++--
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 23 +++++++++++++++++------
>  3 files changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index bb07b9b01e36..5ce49503fcd8 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -145,6 +145,7 @@ extern bool rdt_alloc_capable;
>  extern bool rdt_mon_capable;
>  extern unsigned int rdt_mon_features;
>  extern struct list_head resctrl_schema_all;
> +extern bool resctrl_mounted;
>  
>  enum rdt_group_type {
>  	RDTCTRL_GROUP = 0,
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 1ca8db8c82cc..843df6f64e0e 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -837,7 +837,11 @@ void mbm_handle_overflow(struct work_struct *work)
>  
>  	mutex_lock(&rdtgroup_mutex);
>  
> -	if (!static_branch_likely(&rdt_mon_enable_key))
> +	/*
> +	 * If the filesystem has been unmounted this work no longer needs to
> +	 * run.
> +	 */
> +	if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
>  		goto out_unlock;
>  
>  	r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> @@ -870,7 +874,11 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
>  	unsigned long delay = msecs_to_jiffies(delay_ms);
>  	int cpu;
>  
> -	if (!static_branch_likely(&rdt_mon_enable_key))
> +	/*
> +	 * When a domain comes online there is no guarantee the filesystem is
> +	 * mounted. If not, there is no need to catch counter overflow.
> +	 */
> +	if (!resctrl_mounted || !static_branch_likely(&rdt_mon_enable_key))
>  		return;
>  	cpu = cpumask_any_housekeeping(&dom->cpu_mask);
>  	dom->mbm_work_cpu = cpu;
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index fe6dfea471f2..9ce1f981c8e1 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -42,6 +42,9 @@ LIST_HEAD(rdt_all_groups);
>  /* list of entries for the schemata file */
>  LIST_HEAD(resctrl_schema_all);
>  
> +/* The filesystem can only be mounted once. */
> +bool resctrl_mounted;
> +
>  /* Kernel fs node for "info" directory under root */
>  static struct kernfs_node *kn_info;
>  
> @@ -881,7 +884,7 @@ int proc_resctrl_show(struct seq_file *s, struct pid_namespace *ns,
>  	mutex_lock(&rdtgroup_mutex);
>  
>  	/* Return empty if resctrl has not been mounted. */
> -	if (!static_branch_unlikely(&rdt_enable_key)) {
> +	if (!resctrl_mounted) {
>  		seq_puts(s, "res:\nmon:\n");
>  		goto unlock;
>  	}
> @@ -2613,7 +2616,7 @@ static int rdt_get_tree(struct fs_context *fc)
>  	/*
>  	 * resctrl file system can only be mounted once.
>  	 */
> -	if (static_branch_unlikely(&rdt_enable_key)) {
> +	if (resctrl_mounted) {
>  		ret = -EBUSY;
>  		goto out;
>  	}
> @@ -2674,8 +2677,10 @@ static int rdt_get_tree(struct fs_context *fc)
>  	if (rdt_mon_capable)
>  		static_branch_enable_cpuslocked(&rdt_mon_enable_key);
>  
> -	if (rdt_alloc_capable || rdt_mon_capable)
> +	if (rdt_alloc_capable || rdt_mon_capable) {
>  		static_branch_enable_cpuslocked(&rdt_enable_key);
> +		resctrl_mounted = true;
> +	}
>  
>  	if (is_mbm_enabled()) {
>  		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> @@ -2949,6 +2954,7 @@ static void rdt_kill_sb(struct super_block *sb)
>  	static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
>  	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
>  	static_branch_disable_cpuslocked(&rdt_enable_key);
> +	resctrl_mounted = false;
>  	kernfs_kill_sb(sb);
>  	mutex_unlock(&rdtgroup_mutex);
>  	cpus_read_unlock();
> @@ -3918,7 +3924,7 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
>  	 * If resctrl is mounted, remove all the
>  	 * per domain monitor data directories.
>  	 */
> -	if (static_branch_unlikely(&rdt_mon_enable_key))
> +	if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
>  		rmdir_mondata_subdir_allrdtgrp(r, d->id);
>  
>  	if (is_mbm_enabled())
> @@ -3995,8 +4001,13 @@ int resctrl_online_domain(struct rdt_resource *r, struct rdt_domain *d)
>  	if (is_llc_occupancy_enabled())
>  		INIT_DELAYED_WORK(&d->cqm_limbo, cqm_handle_limbo);
>  
> -	/* If resctrl is mounted, add per domain monitor data directories. */
> -	if (static_branch_unlikely(&rdt_mon_enable_key))
> +	/*
> +	 * If the filesystem is not mounted then only the default resource group
> +	 * exists. Creation of its directories is deferred until mount time
> +	 * by rdt_get_tree() calling mkdir_mondata_all().
> +	 * If resctrl is mounted, add per domain monitor data directories.
> +	 */
> +	if (resctrl_mounted && static_branch_unlikely(&rdt_mon_enable_key))
>  		mkdir_mondata_subdir_allrdtgrp(r, d);
>  
>  	return 0;

-- 
Thanks
Babu Moger