[RFC PATCH 0/2] workqueue: Introduce PF_WQ_RESCUE_WORKER

[Aaron Tomlin <atomlin@atomlin.com>]

The Linux kernel does not provide a way to differentiate between a
kworker and a rescue kworker for user-mode.
From user-mode, one can establish if a task is a kworker by testing for
PF_WQ_WORKER in a specified task's flags bit mask (or bitmap) via
/proc/[PID]/stat. Indeed, one can examine /proc/[PID]/stack and search
for the function namely "rescuer_thread". This is only available to the
root user.

It can be useful to identify a rescue kworker since their CPU affinity
cannot be modified and their initial CPU assignment can be safely ignored.
Furthermore, a workqueue that was created with WQ_MEM_RECLAIM and
WQ_SYSFS the cpumask file is not applicable to the rescue kworker.
By design a rescue kworker should run anywhere.

This patch series introduces PF_WQ_RESCUE_WORKER and ensures it is set and
cleared appropriately and simplifies current_is_workqueue_rescuer().

Aaron Tomlin (2):
  workqueue: Introduce PF_WQ_RESCUE_WORKER
  workqueue: Simplify current_is_workqueue_rescuer()

 include/linux/sched.h |  2 +-
 kernel/workqueue.c    | 25 +++++++++++++++----------
 2 files changed, 16 insertions(+), 11 deletions(-)

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2.39.1