[PATCH v4 0/5] task_struct: extend task comm from 16 to 24 for CONFIG_BASE_FULL

[Yafang Shao]

This patchset changes files among many subsystems. I don't know which
tree it should be applied to, so I just base it on Linus's tree.

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.

After this patchset, the truncated kthreads listed above will be
displayed as:

    rcu_tasks_kthread
    rcu_tasks_rude_kthread
    rcu_tasks_trace_kthread
    poll_mpt3sas0_statu
    ext4-rsv-conversion
    xfs-reclaim/sdf1
    xfs-blockgc/sdf1
    xfs-inodegc/sdf1
    audit_send_reply
    ecryptfs-kthread
    vfio-irqfd-cleanup
    jbd2/nvme0n1p2-8

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 v3:
- fixes -Wstringop-truncation warning reported by kernel test robot

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 (5):
  elfcore: use TASK_COMM_LEN instead of 16 in prpsinfo
  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/elfcore-compat.h | 2 +-
 include/linux/elfcore.h        | 4 ++--
 include/linux/sched.h          | 4 ++++
 kernel/kthread.c               | 7 ++++++-
 6 files changed, 18 insertions(+), 6 deletions(-)

-- 
2.17.1