linux-kernel - [PATCH 0/5] posix-cpu-timers: Graceful handling of reaped processes

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Date:   Fri, 28 Feb 2020 11:07:56 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 0/5] posix-cpu-timers: Graceful handling of reaped processes

Oleg, Thomas,

The posic cpu timer code does not handle processes that is is using as a
clock source exiting and being reaped at all well.  In most cases the
code pins the entire task struct for no good reason.  In the
multi-threaded exec case where the thread group leader exits but the
thread group remains the posix cpu timers just stop working when it
should not.

To solve that problems requires checking if the target processes is
still alive before proceeding.  Replacing cpu.task with a struct pid
pointer is the easiest way I can see to add that extra checking and
extra indirection needed.

So here is my fix.  Oleg, Thomas and if you guys could take a look and
see I made any mistakes I would appreciate it.

Thomas if you want these changes you can have them otherwise I will take
them through my tree.  

Eric W. Biederman (5):
      posix-cpu-timers: cpu_clock_sample_group no longer needs siglock
      posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group
      posix-cpu-timers: Pass the task into arm_timer
      posix-cpu-timers: Store a reference to a pid not a task
      posix-cpu-timers: Stop disabling timers on mt-exec

 include/linux/posix-timers.h   |   2 +-
 kernel/exit.c                  |  11 +---
 kernel/time/posix-cpu-timers.c | 137 +++++++++++++++++++----------------------
 3 files changed, 67 insertions(+), 83 deletions(-)

Eric