linux-kernel - [PATCH 0/5] kthread: increase the size of kthread's comm

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Message-Id: <20210929115036.4851-1-laoar.shao@gmail.com>
Date:   Wed, 29 Sep 2021 11:50:31 +0000
From:   Yafang Shao <laoar.shao@...il.com>
To:     akpm@...ux-foundation.org, pmladek@...e.com, peterz@...radead.org,
        valentin.schneider@....com, keescook@...omium.org,
        mathieu.desnoyers@...icios.com, qiang.zhang@...driver.com,
        robdclark@...omium.org, viro@...iv.linux.org.uk,
        christian@...uner.io, dietmar.eggemann@....com
Cc:     linux-kernel@...r.kernel.org, Yafang Shao <laoar.shao@...il.com>
Subject: [PATCH 0/5] kthread: increase the size of kthread's comm

When I was implementing a new kthread cfs_migration [1], I found the
comm of it is trucated due to the limitation of TASK_COMM_LEN. After I
checked the other kthreads, I found some of them are also truncated, for
example,

    rcu_tasks_kthre
    rcu_tasks_rude_
    rcu_tasks_trace
    ecryptfs-kthrea
    vfio-irqfd-clea
    ext4-rsv-conver
    jbd2/nvme0n1p2-
    ...
    
Besides the in-tree kthreads listed above, the out-of-tree kthreads may
also be trucated, for example,
    
    rtase_work_queu
    nvidia-modeset/
    UVM global queu
    UVM deferred re
    ...
    
That motivates me to do this improvement.

This patch increases the size of ktread's comm from 16 to 24, which is
the same with workqueue's. After this change, the name of kthread can be
fully displayed in /proc/[pid]/comm, for example,
    
    rcu_tasks_kthread
    rcu_tasks_rude_kthread
    rcu_tasks_trace_kthread
    ecryptfs-kthread
    vfio-irqfd-cleanup
    ext4-rsv-conversion
    jbd2/nvme0n1p2-8
    ...
    
Because there're only a few of kthreads, so it won't increase too much
memory consumption.

After this improvement, if the comm of a kthread is still trucated, a
warning will be displayed. Below is the result of my test case -

__kthread_create_on_node:410: comm of pid 14 is truncated from "I-am-a-kthread-with-long-name" to "I-am-a-kthread-with-lon"

[1]. https://lore.kernel.org/lkml/YMmlAP%2FQhE6SWhCF@hirez.programming.kicks-ass.net/

Yafang Shao (5):
  kernel: replace sizeof(task->comm) with TASK_COMM_LEN
  kernel/fork: allocate task->comm dynamicly
  kernel/sched: improve the BUILD_BUG_ON() in get_task_comm()
  kernel: increase the size of kthread's comm
  kernel/kthread: show a warning if kthread's comm is still trucated

 arch/ia64/kernel/mca.c         |  6 +++---
 drivers/block/drbd/drbd_main.c |  2 +-
 drivers/hwtracing/stm/core.c   |  2 +-
 drivers/tty/tty_audit.c        |  2 +-
 fs/exec.c                      |  5 ++++-
 include/linux/sched.h          |  6 ++++--
 kernel/audit.c                 |  4 ++--
 kernel/auditsc.c               |  4 ++--
 kernel/capability.c            |  4 ++--
 kernel/fork.c                  | 26 ++++++++++++++++++++++++++
 kernel/futex.c                 |  2 +-
 kernel/kthread.c               |  8 ++++++--
 kernel/sys.c                   |  2 +-
 kernel/trace/blktrace.c        |  2 +-
 security/lsm_audit.c           |  4 ++--
 security/selinux/selinuxfs.c   |  2 +-
 security/yama/yama_lsm.c       |  2 +-
 sound/core/oss/pcm_oss.c       |  2 +-
 18 files changed, 60 insertions(+), 25 deletions(-)

-- 
2.17.1