[PATCH v7 0/4] Add support for long task name

[Bhupesh <bhupesh@igalia.com>]

Changes since v6:
================
- v6 can be seen here: https://lore.kernel.org/all/20250724123612.206110-1-bhupesh@igalia.com/
- As suggested by Linus, we got rid of 'get_task_comm()' entirely and replaced it with
  'strscpy_pad()' implementation.
- Also changed the current memcpy() use-cases which use 'current->comm' to copy the task name over
  to local copies, to call a wrappper like "get_task_array()".
- Collected 'Reviewed-by' from Kees for [PATCH 1/4].

Changes since v5:
================
- v5 can be seen here: https://lore.kernel.org/lkml/20250716123916.511889-1-bhupesh@igalia.com/ 
- As suggested by Linus, replaced 'tsk->comm' with 'tsk->comm_str' locally, and verified basic
  thread names and then changed 'tsk->comm_str' back to 'tsk->comm'. So essentially now 'tsk->comm'
  is TASK_COMM_EXT_LEN i.e. 64-bytes long.

Changes since v4:
================
- v4 can be seen here: https://lore.kernel.org/lkml/20250521062337.53262-1-bhupesh@igalia.com/ 
- As suggested by Kees, replaced tsk->comm with tsk->comm_str, inside 'task_struct'
  where TASK_COMM_EXT_LEN is 64-bytes.

Changes since v3:
================
- v3 can be seen here: https://lore.kernel.org/lkml/20250507110444.963779-1-bhupesh@igalia.com/
- As suggested by Petr and Steven, used 'comm_ext' name instead of
  'real_comm'. Correspondingly the macro name is changed to 'TASK_COMM_EXT_LEN'
  for the 64-byte extended comm.
- Rebased this patchset on linux-next/master, which contain the following patch from
  Steven now:
       155fd6c3e2f0 ("tracing/sched: Use __string() instead of fixed lengths for task->comm")
- Accordingly, v4 drops the changes done for 'trace/sched' events in v3,
  but retains the 'safe' memcpy' changes for other kernel trace users.

Changes since v2:
================
- v2 can be seen here: https://lore.kernel.org/lkml/20250331121820.455916-1-bhupesh@igalia.com/
- As suggested by Yafang and Kees, picked Linus' suggested approach for
  this version (see: <https://lore.kernel.org/all/CAHk-=wjAmmHUg6vho1KjzQi2=psR30+CogFd4aXrThr2gsiS4g@mail.gmail.com/>).
- Dropped kthreads patch from this version. It would be sent out
  separately, if we have a consensus on this approach.

Changes since v1:
================
- v1 can be seen here: https://lore.kernel.org/lkml/20250314052715.610377-1-bhupesh@igalia.com/
- As suggested by Kees, added [PATCH 3/3] to have a consistent
  'full_name' entry inside 'task_struct' which both tasks and
  kthreads can use.
- Fixed the commit message to indicate that the existing ABI
  '/proc/$pid/task/$tid/comm' remains untouched and a parallel
  '/proc/$pid/task/$tid/full_name' ABI for new (interested) users.

While working with user-space debugging tools which work especially
on linux gaming platforms, I found that the task name is truncated due
to the limitation of TASK_COMM_LEN.

Now, during debug tracing, seeing truncated names is not very useful,
especially on gaming platforms where the number of tasks running can
be very high.

This patchset does not touch 'TASK_COMM_LEN' at all, i.e.
'TASK_COMM_LEN' and the 16-byte design remains untouched.

Via this patchset, Linus suggested 'tsk->comm' is made 64-byte long
and equal to TASK_COMM_EXT_LEN.

To avoid any surprises / bug,s I replaced 'tsk->comm' with
'tsk->comm_str' locally inside 'task_struct' and checked compilation
of code and basic working of thread names:

       struct task_struct {
	       ..............
               char    comm_str[TASK_COMM_EXT_LEN];
	       ..............
       };

       where TASK_COMM_EXT_LEN is 64-bytes.

Once done, I changed the name back to 'tsk->comm'.

To ensure that the existing ABI and userspace continues to work
as intended, we ensure that:

- Existing users of 'get_task_comm'/ 'set_task_comm' will get 'tsk->comm'
  truncated to a maximum of 'TASK_COMM_LEN' (16-bytes) to maintain ABI,
- New / Modified users of 'get_task_comm'/ 'set_task_comm' will get
 'tsk->comm' supported up to a maximum of 'TASK_COMM_EXT_LEN' (64-bytes).

Note, that the existing users have not been modified to migrate to
'TASK_COMM_EXT_LEN', in case they have hard-coded expectations of
dealing with only a 'TASK_COMM_LEN' long 'tsk->comm_str'.

After this change, gdb is able to show full name of the task, using a
simple app which generates threads with long names [see 1]:
  # gdb ./threadnames -ex "run info thread" -ex "detach" -ex "quit" > log
  # cat log

  NameThatIsTooLongForComm[4662]

[1]. https://github.com/lostgoat/tasknames

Bhupesh (4):
  exec: Remove obsolete comments
  include: Set tsk->comm length to 64 bytes
  treewide: Replace 'get_task_comm()' with 'strscpy_pad()'
  treewide: Switch memcpy() users of 'task->comm' to a more safer
    implementation

 drivers/connector/cn_proc.c                   |  2 +-
 drivers/dma-buf/sw_sync.c                     |  2 +-
 .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_fence.c  |  2 +-
 .../drm/amd/amdgpu/amdgpu_eviction_fence.c    |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c       |  2 +-
 .../gpu/drm/amd/amdgpu/amdgpu_userq_fence.c   |  2 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c        |  4 +-
 drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c  |  2 +-
 drivers/gpu/drm/lima/lima_ctx.c               |  2 +-
 drivers/gpu/drm/panfrost/panfrost_gem.c       |  2 +-
 drivers/gpu/drm/panthor/panthor_gem.c         |  2 +-
 drivers/gpu/drm/virtio/virtgpu_ioctl.c        |  2 +-
 drivers/hwtracing/stm/core.c                  |  2 +-
 drivers/tty/tty_audit.c                       |  2 +-
 fs/bcachefs/thread_with_file.c                |  2 +-
 fs/binfmt_elf.c                               |  2 +-
 fs/binfmt_elf_fdpic.c                         |  2 +-
 fs/ocfs2/cluster/netdebug.c                   |  1 -
 fs/proc/array.c                               |  2 +-
 include/linux/coredump.h                      |  2 +-
 include/linux/sched.h                         | 50 ++++++++++++-------
 include/linux/tracepoint.h                    |  4 +-
 include/trace/events/block.h                  | 10 ++--
 include/trace/events/oom.h                    |  2 +-
 include/trace/events/osnoise.h                |  2 +-
 include/trace/events/sched.h                  | 13 +++--
 include/trace/events/signal.h                 |  2 +-
 include/trace/events/task.h                   |  4 +-
 kernel/audit.c                                |  6 ++-
 kernel/auditsc.c                              |  6 ++-
 kernel/sys.c                                  |  2 +-
 mm/kmemleak.c                                 |  6 ---
 net/bluetooth/hci_sock.c                      |  2 +-
 net/netfilter/nf_tables_api.c                 |  2 +-
 security/integrity/integrity_audit.c          |  3 +-
 security/ipe/audit.c                          |  2 +-
 security/landlock/domain.c                    |  2 +-
 security/lsm_audit.c                          |  7 +--
 tools/bpf/bpftool/pids.c                      |  6 +--
 .../bpf/test_kmods/bpf_testmod-events.h       |  2 +-
 40 files changed, 91 insertions(+), 83 deletions(-)

-- 
2.38.1