Re: [PATCH v6 04/24] x86/resctrl: Move rmid allocation out of mkdir_rdt_prepare()

Moger, Babu
2023-10-04T18:01:18Z

Hi James,

On 9/14/23 12:21, James Morse wrote:
> RMID are allocated for each monitor or control group directory, because
> each of these needs its own RMID. For control groups,
> rdtgroup_mkdir_ctrl_mon() later goes on to allocate the CLOSID.
>
> MPAM's equivalent of RMID is not an independent number, so can't be
> allocated until the CLOSID is known. An RMID allocation for one CLOSID
> may fail, whereas another may succeed depending on how many monitor
> groups a control group has.
>
> The RMID allocation needs to move to be after the CLOSID has been
> allocated.
>
> Move the RMID allocation out of mkdir_rdt_prepare() to occur in its caller,
> after the mkdir_rdt_prepare() call. This allows the RMID allocator to
> know the CLOSID.
>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Tested-By: Peter Newman <peternewman@google.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v2:
> * Moved kernfs_activate() later to preserve atomicity of files being visible
>
> Changes since v5:
> * Renamed out_id_free as out_closid_free.
> ---
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 35 +++++++++++++++++++-------
> 1 file changed, 26 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 7a7369a323b5..d25cb8c9a20e 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3189,6 +3189,12 @@ static int mkdir_rdt_prepare_rmid_alloc(struct rdtgroup *rdtgrp)
> return 0;
> }
>
> +static void mkdir_rdt_prepare_rmid_free(struct rdtgroup *rgrp)
> +{
> + if (rdt_mon_capable)
> + free_rmid(rgrp->mon.rmid);
> +}
> +
> static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
> const char *name, umode_t mode,
> enum rdt_group_type rtype, struct rdtgroup **r)
> @@ -3254,12 +3260,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
> goto out_destroy;
> }
>
> - ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> - if (ret)
> - goto out_destroy;
> -
> - kernfs_activate(kn);

You should not remove "kernfs_activate(kn); from here (only the last line).

kernfs_create_dir is called in this function.

/* kernfs creates the directory for rdtgrp */
kn = kernfs_create_dir(parent_kn, name, mode, rdtgrp);

There should be matching kernfs_activate.

> -
> /*
> * The caller unlocks the parent_kn upon success.
> */
> @@ -3278,7 +3278,6 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
> static void mkdir_rdt_prepare_clean(struct rdtgroup *rgrp)
> {
> kernfs_remove(rgrp->kn);
> - free_rmid(rgrp->mon.rmid);
> rdtgroup_remove(rgrp);
> }
>
> @@ -3300,12 +3299,21 @@ static int rdtgroup_mkdir_mon(struct kernfs_node *parent_kn,
> prgrp = rdtgrp->mon.parent;
> rdtgrp->closid = prgrp->closid;
>
> + ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> + if (ret) {
> + mkdir_rdt_prepare_clean(rdtgrp);
> + goto out_unlock;
> + }
> +
> + kernfs_activate(rdtgrp->kn);

I dont see the need for this. There is kernfs_activate inside
mkdir_rdt_prepare_rmid_alloc (mkdir_rdt_prepare_rmid_alloc
->mkdir_mondata_all) for all the files created.
Also mkdir_rdt_prepare already has kernfs_activate for the files it created.

> +
> /*
> * Add the rdtgrp to the list of rdtgrps the parent
> * ctrl_mon group has to track.
> */
> list_add_tail(&rdtgrp->mon.crdtgrp_list, &prgrp->mon.crdtgrp_list);
>
> +out_unlock:
> rdtgroup_kn_unlock(parent_kn);
> return ret;
> }
> @@ -3336,9 +3344,16 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
> ret = 0;
>
> rdtgrp->closid = closid;
> +
> + ret = mkdir_rdt_prepare_rmid_alloc(rdtgrp);
> + if (ret)
> + goto out_closid_free;
> +
> + kernfs_activate(rdtgrp->kn);
> +

Same as above.

> ret = rdtgroup_init_alloc(rdtgrp);
> if (ret < 0)
> - goto out_id_free;
> + goto out_rmid_free;
>
> list_add(&rdtgrp->rdtgroup_list, &rdt_all_groups);
>
> @@ -3358,7 +3373,9 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
>
> out_del_list:
> list_del(&rdtgrp->rdtgroup_list);
> -out_id_free:
> +out_rmid_free:
> + mkdir_rdt_prepare_rmid_free(rdtgrp);
> +out_closid_free:
> closid_free(closid);
> out_common_fail:
> mkdir_rdt_prepare_clean(rdtgrp);

--
Thanks
Babu Moger