A lockdep fix removed two rdt_last_cmd_clear() calls that were used
to clear the last_cmd_status buffer but called without holding the
required rdtgroup_mutex. The impacted resctrl commands are:
writing to the cpus or cpus_list files and creating a new monitor
or control group. With stale data in the last_cmd_status buffer the
impacted resctrl commands report the stale error on success, or append
its own failure message to the stale error on failure.

Consequently, restore the rdt_last_cmd_clear() calls after acquiring
rdtgroup_mutex.

Fixes: c8eafe149530 ("x86/resctrl: Fix potential lockdep warning")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
---
Changes in v2:
1. Move rdt_last_cmd_clear() to be right after acquiring the mutex.
2. Rewrite the commit message in imperative tone, add explanation of the
   error phenomenon.
Link to v1: https://lore.kernel.org/all/20250529113353.3275066-1-zengheng4@huawei.com/

 fs/resctrl/rdtgroup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index cc37f58b47dd..1beb124e25f6 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -536,6 +536,8 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		goto unlock;
 	}

+	rdt_last_cmd_clear();
+
 	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
 	    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
 		ret = -EINVAL;
@@ -3472,6 +3474,8 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 		goto out_unlock;
 	}

+	rdt_last_cmd_clear();
+
 	/*
 	 * Check that the parent directory for a monitor group is a "mon_groups"
 	 * directory.
--
2.25.1

Hi Zeng Heng,

On 6/3/25 5:58 AM, Zeng Heng wrote:
> A lockdep fix removed two rdt_last_cmd_clear() calls that were used
> to clear the last_cmd_status buffer but called without holding the
> required rdtgroup_mutex. The impacted resctrl commands are:
> writing to the cpus or cpus_list files and creating a new monitor
> or control group. With stale data in the last_cmd_status buffer the
> impacted resctrl commands report the stale error on success, or append
> its own failure message to the stale error on failure.
> 
> Consequently, restore the rdt_last_cmd_clear() calls after acquiring
> rdtgroup_mutex.
> 
> Fixes: c8eafe149530 ("x86/resctrl: Fix potential lockdep warning")
> Signed-off-by: Zeng Heng <zengheng4@huawei.com>
> ---

Thank you.

Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>

Reinette

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     dd2922dcfaa3296846265e113309e5f7f138839f
Gitweb:        https://git.kernel.org/tip/dd2922dcfaa3296846265e113309e5f7f138839f
Author:        Zeng Heng <zengheng4@huawei.com>
AuthorDate:    Tue, 03 Jun 2025 20:58:28 +08:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 04 Jun 2025 20:32:55 +02:00

fs/resctrl: Restore the rdt_last_cmd_clear() calls after acquiring rdtgroup_mutex

A lockdep fix removed two rdt_last_cmd_clear() calls that were used to
clear the last_cmd_status buffer but called without holding the required
rdtgroup_mutex.

The impacted resctrl commands are writing to the cpus or cpus_list files
and creating a new monitor or control group. With stale data in the
last_cmd_status buffer the impacted resctrl commands report the stale error
on success, or append its own failure message to the stale error on
failure.

Consequently, restore the rdt_last_cmd_clear() calls after acquiring
rdtgroup_mutex.

Fixes: c8eafe149530 ("x86/resctrl: Fix potential lockdep warning")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/all/20250603125828.1590067-1-zengheng4@huawei.com
---
 fs/resctrl/rdtgroup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index cc37f58..1beb124 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -536,6 +536,8 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		goto unlock;
 	}
 
+	rdt_last_cmd_clear();
+
 	if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED ||
 	    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
 		ret = -EINVAL;
@@ -3472,6 +3474,8 @@ static int mkdir_rdt_prepare(struct kernfs_node *parent_kn,
 		goto out_unlock;
 	}
 
+	rdt_last_cmd_clear();
+
 	/*
 	 * Check that the parent directory for a monitor group is a "mon_groups"
 	 * directory.