[PATCH v3 0/4] task_struct: extend task comm from 16 to 24 for CONFIG_BASE_FULL

[Yafang Shao <laoar.shao@gmail.com>]

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-
    xfs-reclaim/sdf

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-
    ...

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 v2:
- avoid change UAPI code per Kees
- remove the description of out of tree code from commit log per Peter

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

Yafang Shao (4):
  connector: use __get_task_comm in proc_comm_connector
  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

 drivers/connector/cn_proc.c | 5 ++++-
 fs/exec.c                   | 2 +-
 include/linux/sched.h       | 4 ++++
 kernel/kthread.c            | 7 ++++++-
 4 files changed, 15 insertions(+), 3 deletions(-)

-- 
2.18.2