[PATCH v2 0/5] 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

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 did some basic testing and found the problems I explained here:
https://lore.kernel.org/io-uring/F3B6EA77-99D1-4424-85AC-CFFED7DC6A4B@kernel.dk/T/#t
They appear with and without my changes.

Changes in v2:

- I dropped/deferred these changes:
  - 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()

Stefan Metzmacher (5):
  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()
  fs/proc: hide PF_IO_WORKER in get_task_cmdline()

 fs/io-wq.c     | 17 +++++++++--------
 fs/io_uring.c  | 22 +++++++++++-----------
 fs/proc/base.c |  3 +++
 kernel/fork.c  |  1 +
 4 files changed, 24 insertions(+), 19 deletions(-)

-- 
2.25.1