[PATCH 2/2] fs/proc: Show the content of task->user_cpus_ptr in /proc/<pid>/status

[Waiman Long]

The task->user_cpus_ptr was introduced by commit b90ca8badbd1 ("sched:
Introduce task_struct::user_cpus_ptr to track requested affinity") to
keep track of user-requested CPU affinity. With commit da019032819a
("sched: Enforce user requested affinity"), user_cpus_ptr will
persistently affect how cpus_allowed will be set. So it makes sense to
enable users to see the presence of a previously set user_cpus_ptr so
they can do something about it without getting a surprise.

Add new "Cpus_user" and "Cpus_user_list" fields to /proc/<pid>/status
output via task_cpus_allowed() as the presence of user_cpus_ptr will
affect the cpus_allowed cpumask.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 Documentation/filesystems/proc.rst | 2 ++
 fs/proc/array.c                    | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 2971551b7235..fb9e7753010c 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -311,6 +311,8 @@ It's slow but very precise.
  SpeculationIndirectBranch   indirect branch speculation mode
  Cpus_allowed                mask of CPUs on which this process may run
  Cpus_allowed_list           Same as previous, but in "list format"
+ Cpus_user                   mask of user requested CPUs from sched_setaffinity(2)
+ Cpus_user_list              Same as previous, but in "list format"
  Mems_allowed                mask of memory nodes allowed to this process
  Mems_allowed_list           Same as previous, but in "list format"
  voluntary_ctxt_switches     number of voluntary context switches
diff --git a/fs/proc/array.c b/fs/proc/array.c
index d6a0369caa93..30ceab935e13 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -405,10 +405,19 @@ static inline void task_context_switch_counts(struct seq_file *m,
 
 static void task_cpus_allowed(struct seq_file *m, struct task_struct *task)
 {
+	cpumask_t *user_cpus = task->user_cpus_ptr;
+
 	seq_printf(m, "Cpus_allowed:\t%*pb\n",
 		   cpumask_pr_args(&task->cpus_mask));
 	seq_printf(m, "Cpus_allowed_list:\t%*pbl\n",
 		   cpumask_pr_args(&task->cpus_mask));
+
+	if (user_cpus) {
+		seq_printf(m, "Cpus_user:\t%*pb\n", cpumask_pr_args(user_cpus));
+		seq_printf(m, "Cpus_user_list:\t%*pbl\n", cpumask_pr_args(user_cpus));
+	} else {
+		seq_puts(m, "Cpus_user:\nCpus_user_list:\n");
+	}
 }
 
 static inline void task_core_dumping(struct seq_file *m, struct task_struct *task)
-- 
2.51.0