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Date: Fri, 14 Jul 2023 11:26:50 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc: fenghua.yu@...el.com, dave.hansen@...ux.intel.com, x86@...nel.org,
hpa@...or.com, paulmck@...nel.org, akpm@...ux-foundation.org,
quic_neeraju@...cinc.com, rdunlap@...radead.org,
damien.lemoal@...nsource.wdc.com, songmuchun@...edance.com,
peterz@...radead.org, jpoimboe@...nel.org, pbonzini@...hat.com,
chang.seok.bae@...el.com, pawan.kumar.gupta@...ux.intel.com,
jmattson@...gle.com, daniel.sneddon@...ux.intel.com,
sandipan.das@....com, tony.luck@...el.com, james.morse@....com,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
bagasdotme@...il.com, eranian@...gle.com,
christophe.leroy@...roup.eu, jarkko@...nel.org,
adrian.hunter@...el.com, quic_jiles@...cinc.com,
peternewman@...gle.com
Subject: Re: [PATCH v5 7/8] x86/resctrl: Move default control group creation
during mount
Hi Reinette,
Sorry.. Took a while to respond. I had to recreate the issue to refresh my
memory.
On 7/7/23 16:46, Reinette Chatre wrote:
> Hi Babu,
>
> On 6/1/2023 12:02 PM, Babu Moger wrote:
>> Currently, the resctrl default control group is created during kernel
>> init time and rest of the files are added during mount. If the new
>
> Please drop the word "Currently"
Sure
>
>> files are to be added to the default group during the mount then it
>> has to be done separately again.
>>
>> This can avoided if all the files are created during the mount and
>> destroyed during the umount. Move the default group creation in
>
> "creation in" -> "creation to"?
Sure
>
>> rdt_get_tree and removal in rdt_kill_sb.
>
> I think it would be simpler if this patch is moved earlier in series
> then patch 8 can more easily be squashed where appropriate.
Yes, I was thinking about that.
>
>>
>> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 59 ++++++++++++++++----------------
>> 1 file changed, 30 insertions(+), 29 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 2f5cdc638607..e03cb01c4742 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -57,6 +57,7 @@ static char last_cmd_status_buf[512];
>> struct dentry *debugfs_resctrl;
>>
>> static bool resctrl_debug;
>> +static int rdtgroup_setup_root(void);
>>
>> void rdt_last_cmd_clear(void)
>> {
>> @@ -2515,13 +2516,6 @@ static int rdt_get_tree(struct fs_context *fc)
>>
>> cpus_read_lock();
>> mutex_lock(&rdtgroup_mutex);
>> - /*
>> - * resctrl file system can only be mounted once.
>> - */
>> - if (static_branch_unlikely(&rdt_enable_key)) {
>> - ret = -EBUSY;
>> - goto out;
>> - }
>>
>
> This change is unexpected.
Please see my comments below.
>
>> ret = rdt_enable_ctx(ctx);
>> if (ret < 0)
>> @@ -2535,9 +2529,15 @@ static int rdt_get_tree(struct fs_context *fc)
>>
>> closid_init();
>>
>> + ret = rdtgroup_add_files(rdtgroup_default.kn, RFTYPE_CTRL_BASE);
>> + if (ret)
>> + goto out_schemata_free;
>> +
>> + kernfs_activate(rdtgroup_default.kn);
>> +
>> ret = rdtgroup_create_info_dir(rdtgroup_default.kn);
>> if (ret < 0)
>> - goto out_schemata_free;
>> + goto out_default;
>>
>> if (rdt_mon_capable) {
>> ret = mongroup_create_dir(rdtgroup_default.kn,
>> @@ -2587,6 +2587,8 @@ static int rdt_get_tree(struct fs_context *fc)
>> kernfs_remove(kn_mongrp);
>> out_info:
>> kernfs_remove(kn_info);
>> +out_default:
>> + kernfs_remove(rdtgroup_default.kn);
>> out_schemata_free:
>> schemata_list_destroy();
>> out_mba:
>> @@ -2664,10 +2666,23 @@ static const struct fs_context_operations rdt_fs_context_ops = {
>> static int rdt_init_fs_context(struct fs_context *fc)
>> {
>> struct rdt_fs_context *ctx;
>> + int ret;
>> +
>> + /*
>> + * resctrl file system can only be mounted once.
>> + */
>> + if (static_branch_unlikely(&rdt_enable_key))
>> + return -EBUSY;
>> +
>> + ret = rdtgroup_setup_root();
>> + if (ret)
>> + return ret;
>>
>
> Why was it necessary to move this code?
Please see my comments below..
>
>> ctx = kzalloc(sizeof(struct rdt_fs_context), GFP_KERNEL);
>> - if (!ctx)
>> + if (!ctx) {
>> + kernfs_destroy_root(rdt_root);
>> return -ENOMEM;
>> + }
>>
>> ctx->kfc.root = rdt_root;
>> ctx->kfc.magic = RDTGROUP_SUPER_MAGIC;
>> @@ -2845,6 +2860,9 @@ 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);
>> + /* Remove the default group and cleanup the root */
>> + list_del(&rdtgroup_default.rdtgroup_list);
>> + kernfs_destroy_root(rdt_root);
>
> Why not just add kernfs_remove(rdtgroup_default.kn) to rmdir_all_sub()?
List rdtgroup_default.rdtgroup_list is added during the mount and had to
be removed during umount and rdt_root is destroyed here.
Please see more comments below.
>
>> kernfs_kill_sb(sb);
>> mutex_unlock(&rdtgroup_mutex);
>> cpus_read_unlock();
>> @@ -3598,10 +3616,8 @@ static struct kernfs_syscall_ops rdtgroup_kf_syscall_ops = {
>> .show_options = rdtgroup_show_options,
>> };
>>
>> -static int __init rdtgroup_setup_root(void)
>> +static int rdtgroup_setup_root(void)
>> {
>> - int ret;
>> -
>> rdt_root = kernfs_create_root(&rdtgroup_kf_syscall_ops,
>> KERNFS_ROOT_CREATE_DEACTIVATED |
>> KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK,
>> @@ -3618,19 +3634,11 @@ static int __init rdtgroup_setup_root(void)
>>
>> list_add(&rdtgroup_default.rdtgroup_list, &rdt_all_groups);
>>
>> - ret = rdtgroup_add_files(kernfs_root_to_node(rdt_root), RFTYPE_CTRL_BASE);
>> - if (ret) {
>> - kernfs_destroy_root(rdt_root);
>> - goto out;
>> - }
>> -
>> rdtgroup_default.kn = kernfs_root_to_node(rdt_root);
>> - kernfs_activate(rdtgroup_default.kn);
>>
>> -out:
>> mutex_unlock(&rdtgroup_mutex);
>>
>> - return ret;
>> + return 0;
>> }
>>
>> static void domain_destroy_mon_state(struct rdt_domain *d)
>> @@ -3752,13 +3760,9 @@ int __init rdtgroup_init(void)
>> seq_buf_init(&last_cmd_status, last_cmd_status_buf,
>> sizeof(last_cmd_status_buf));
>>
>> - ret = rdtgroup_setup_root();
>> - if (ret)
>> - return ret;
>> -
>> ret = sysfs_create_mount_point(fs_kobj, "resctrl");
>> if (ret)
>> - goto cleanup_root;
>> + return ret;
>>
>
> It is not clear to me why this change is required, could you
> please elaborate? It seems that all that is needed is for
> rdtgroup_add_files() to move to rdt_get_tree() (which you have done)
> and then an additional call to kernfs_remove() in rmdir_all_sub().
> I must be missing something, could you please help me understand?
>
Yes. I started with that approach. But there are issues with that approach.
Currently, rdt_root(which is rdtgroup_default.kn) is created during
rdtgroup_init. At the same time the root files are created. Also, default
group is added to rdt_all_groups. Basically, the root files and
rdtgroup_default group is always there even though filesystem is never
mounted. Also mbm_over and cqm_limbo workqueues are always running even
though filesystem is not mounted.
I changed rdtgroup_add_files() to move to rdt_get_tree() and added
kernfs_remove() in rmdir_all_sub(). This caused problems. The
kernfs_remove(rdtgroup_default.kn) removes all the reference counts and
releases the root. When we mount again, we hit this this problem below.
[ 404.558461] ------------[ cut here ]------------
[ 404.563631] WARNING: CPU: 35 PID: 7728 at fs/kernfs/dir.c:522
kernfs_new_node+0x63/0x70
404.778793] ? __warn+0x81/0x140
[ 404.782535] ? kernfs_new_node+0x63/0x70
[ 404.787036] ? report_bug+0x102/0x200
[ 404.791247] ? handle_bug+0x3f/0x70
[ 404.795269] ? exc_invalid_op+0x13/0x60
[ 404.799671] ? asm_exc_invalid_op+0x16/0x20
[ 404.804461] ? kernfs_new_node+0x63/0x70
[ 404.808954] ? snprintf+0x49/0x70
[ 404.812762] __kernfs_create_file+0x30/0xc0
[ 404.817534] rdtgroup_add_files+0x6c/0x100
Basically kernel says your rdt_root is not initialized. That is the reason
I had to move everything to mount time. The rdt_root is created and
initialized during the mount and also destroyed during the umount.
And I had to move rdt_enable_key check during rdt_root creation.
--
Thanks
Babu Moger
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