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: c8eafe1 ("x86/resctrl: Fix potential lockdep warning")
Signed-off-by: Zeng Heng <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Reinette Chatre <[email protected]>
Link: https://lore.kernel.org/all/[email protected]

Author: henryZe

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.