[RFC PATCH 00/10] Complete setup before calling wake_up_new_task() and improve task->comm

[Stefan Metzmacher <metze@samba.org>]

Hi,

now that we have an explicit wake_up_new_task() in order to start the
result from create_io_thread(), we should things up before calling
wake_up_new_task().

There're also some improvements around task->comm:
- We return 0 bytes for /proc/<pid>/cmdline
- We no longer allow a userspace process to change
  /proc/<pid>/[task/<tid>]/comm
- We dynamically generate comm names (up to 63 chars)
  via io_wq_worker_comm(), similar to wq_worker_comm()

While doing this I noticed a few places we check for
PF_KTHREAD, but not PF_IO_WORKER, maybe we should
have something like a PS_IS_KERNEL_THREAD_MASK() macro
that should be used in generic places and only
explicitly use PF_IO_WORKER or PF_KTHREAD checks where the
difference matters.

There are also quite a number of cases where we use
same_thread_group(), I guess these need to be checked.
Should that return true if userspace threads and their iothreds
are compared?

I've compiled but didn't test, I hope there's something useful...

Stefan Metzmacher (10):
  kernel: always initialize task->pf_io_worker to NULL
  io_uring: io_sq_thread() no longer needs to reset
    current->pf_io_worker
  io-wq: call set_task_comm() before wake_up_new_task()
  io_uring: complete sq_thread setup before calling wake_up_new_task()
  io-wq: protect against future set_task_comm() overflows.
  io_uring: protect against future set_task_comm() overflows.
  fs/proc: hide PF_IO_WORKER in get_task_cmdline()
  fs/proc: protect /proc/<pid>/[task/<tid>]/comm for PF_IO_WORKER
  io-wq: add io_wq_worker_comm() helper function for dynamic
    proc_task_comm() generation
  fs/proc: make use of io_wq_worker_comm() for PF_IO_WORKER threads

 fs/io-wq.c      | 118 ++++++++++++++++++++++++++++++++++++++++++++----
 fs/io-wq.h      |   4 ++
 fs/io_uring.c   |  33 +++++++++-----
 fs/proc/array.c |   3 ++
 fs/proc/base.c  |  18 ++++++--
 kernel/fork.c   |   1 +
 6 files changed, 154 insertions(+), 23 deletions(-)

-- 
2.25.1