[PATCH v6 0/3] Add support for long task name

Bhupesh
2025-07-24T12:36:38Z

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 (3):
exec: Remove obsolete comments
treewide: Switch memcpy() users of 'task->comm' to a more safer
implementation
include: Set tsk->comm length to 64 bytes

include/linux/coredump.h | 3 ++-
include/linux/sched.h | 15 +++++++++------
include/trace/events/block.h | 5 +++++
include/trace/events/oom.h | 1 +
include/trace/events/osnoise.h | 1 +
include/trace/events/signal.h | 1 +
include/trace/events/task.h | 2 ++
7 files changed, 21 insertions(+), 7 deletions(-)

--
2.38.1