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From:   Yafang Shao <laoar.shao@gmail.com>
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        akpm@linux-foundation.org, peterz@infradead.org,
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        bristot@redhat.com
Cc:     linux-kernel@vger.kernel.org, Yafang Shao <laoar.shao@gmail.com>
Subject: [PATCH v2 0/4] task_struct: extend task comm from 16 to 24 for CONFIG_BASE_FULL 
Date:   Thu,  7 Oct 2021 12:07:48 +0000
Message-Id: <20211007120752.5195-1-laoar.shao@gmail.com>
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When I was implementing a new per-cpu kthread cfs_migration, I found the
comm of it "cfs_migration/%u" is truncated due to the limitation of
TASK_COMM_LEN. For example, the comm of the percpu thread on CPU10~19 are
all with the same name "cfs_migration/1", which will confuse the user. This
issue is not critical, because we can get the corresponding CPU from the
task's Cpus_allowed. But for kthreads correspoinding to other hardware
devices, it is not easy to get the detailed device info from task comm,
for example,

    jbd2/nvme0n1p2-
    nvidia-modeset/

We can also shorten the name to work around this problem, but I find
there are so many truncated kthreads:

    rcu_tasks_kthre
    rcu_tasks_rude_
    rcu_tasks_trace
    poll_mpt3sas0_s
    ext4-rsv-conver
    xfs-reclaim/sd{a, b, c, ...}
    xfs-blockgc/sd{a, b, c, ...}
    xfs-inodegc/sd{a, b, c, ...}
    audit_send_repl
    ecryptfs-kthrea
    vfio-irqfd-clea
    jbd2/nvme0n1p2-
    ...

Besides the in-tree kthreads listed above, the out-of-tree kthreads may
also be truncated:

    rtase_work_queu
    nvidia-modeset/
    UVM global queu
    UVM deferred re
    ...

We should improve this problem fundamentally.

This patch extends the size of task comm to 24 bytes, which is the
same length with workqueue's, for the CONFIG_BASE_FULL case. And for the
CONFIG_BASE_SMALL case, the size of task comm is still kept as 16 bytes.

If the kthread's comm is still truncated, a warning will be printed.
Below is the result of my test case:

truncated kthread comm:I-am-a-kthread-with-lon, pid:14 by 6 characters

Changes since v1:
- extend task comm to 24bytes, per Petr
- improve the warning per Petr
- make the checkpatch warning a seperate patch

Yafang Shao (4):
  cn_proc.h: use TASK_COMM_LEN instread of 16 in struct proc_event
  fs/exec: use strscpy instead of strlcpy in __set_task_comm
  sched.h: extend task comm from 16 to 24 for CONFIG_BASE_FULL
  kernel/kthread: show a warning if kthread's comm is truncated

 fs/exec.c                    | 2 +-
 include/linux/sched.h        | 4 ++++
 include/uapi/linux/cn_proc.h | 2 +-
 kernel/kthread.c             | 7 ++++++-
 4 files changed, 12 insertions(+), 3 deletions(-)

-- 
2.18.2