x86/resctrl: Only show tasks' pid in current pid namespace

BugLink: https://bugs.launchpad.net/bugs/2032689

[ Upstream commit 2997d94 ]

When writing a task id to the "tasks" file in an rdtgroup,
rdtgroup_tasks_write() treats the pid as a number in the current pid
namespace. But when reading the "tasks" file, rdtgroup_tasks_show() shows
the list of global pids from the init namespace, which is confusing and
incorrect.

To be more robust, let the "tasks" file only show pids in the current pid
namespace.

Fixes: e02737d ("x86/intel_rdt: Add tasks files")
Signed-off-by: Shawn Wang <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Acked-by: Reinette Chatre <[email protected]>
Acked-by: Fenghua Yu <[email protected]>
Tested-by: Reinette Chatre <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Kamal Mostafa <[email protected]>
Signed-off-by: Stefan Bader <[email protected]>

Author: Shawn Wang

arch/x86/kernel/cpu/resctrl/rdtgroup.c

@@ -731,11 +731,15 @@ static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
 static void show_rdt_tasks(struct rdtgroup *r, struct seq_file *s)
 {
 	struct task_struct *p, *t;
+	pid_t pid;
 
 	rcu_read_lock();
 	for_each_process_thread(p, t) {
-		if (is_closid_match(t, r) || is_rmid_match(t, r))
-			seq_printf(s, "%d\n", t->pid);
+		if (is_closid_match(t, r) || is_rmid_match(t, r)) {
+			pid = task_pid_vnr(t);
+			if (pid)
+				seq_printf(s, "%d\n", pid);
+		}
 	}
 	rcu_read_unlock();
 }