[PATCH v5 0/3] Add support for long task name

From: Bhupesh
Date: Wed Jul 16 2025 - 08:40:29 EST

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Changes since v4:
================
- v4 can be seen here: https://lore.kernel.org/lkml/20250507110444.963779-1-bhupesh@xxxxxxxxxx/
- 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@xxxxxxxxxx/
- 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@xxxxxxxxxx/
- As suggested by Yafang and Kees, picked Linus' suggested approach for
this version (see: <https://lore.kernel.org/all/CAHk-=wjAmmHUg6vho1KjzQi2=psR30+CogFd4aXrThr2gsiS4g@xxxxxxxxxxxxxx/>).
- 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@xxxxxxxxxx/
- 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, as Kees suggested 'tsk->comm' is replaced
with 'tsk->comm_str', inside 'task_struct':
union {
char comm_str[TASK_COMM_EXT_LEN];
};

where TASK_COMM_EXT_LEN is 64-bytes.

And then 'get_task_comm()' to pass 'tsk->comm_str'
to the existing users.

This would mean that ABI is maintained while ensuring that:

- Existing users of 'get_task_comm'/ 'set_task_comm' will get 'tsk->comm_str'
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_str' supported for a maximum of 'TASK_COMM_EXTLEN' (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
treewide: Switch from tsk->comm to tsk->comm_str which is 64 bytes
long

arch/arm64/kernel/traps.c | 2 +-
arch/arm64/kvm/mmu.c | 2 +-
block/blk-core.c | 2 +-
block/bsg.c | 2 +-
drivers/char/random.c | 2 +-
drivers/hid/hid-core.c | 6 +++---
drivers/mmc/host/tmio_mmc_core.c | 6 +++---
drivers/pci/pci-sysfs.c | 2 +-
drivers/scsi/scsi_ioctl.c | 2 +-
drivers/tty/serial/serial_core.c | 2 +-
drivers/tty/tty_io.c | 8 ++++----
drivers/usb/core/devio.c | 16 ++++++++--------
drivers/usb/core/message.c | 2 +-
drivers/vfio/group.c | 2 +-
drivers/vfio/vfio_iommu_type1.c | 2 +-
drivers/vfio/vfio_main.c | 2 +-
drivers/xen/evtchn.c | 2 +-
drivers/xen/grant-table.c | 2 +-
fs/binfmt_elf.c | 2 +-
fs/coredump.c | 4 ++--
fs/drop_caches.c | 2 +-
fs/exec.c | 8 ++++----
fs/ext4/dir.c | 2 +-
fs/ext4/inode.c | 2 +-
fs/ext4/namei.c | 2 +-
fs/ext4/super.c | 12 ++++++------
fs/hugetlbfs/inode.c | 2 +-
fs/ioctl.c | 2 +-
fs/iomap/direct-io.c | 2 +-
fs/jbd2/transaction.c | 2 +-
fs/locks.c | 2 +-
fs/netfs/internal.h | 2 +-
fs/proc/base.c | 2 +-
fs/read_write.c | 2 +-
fs/splice.c | 2 +-
include/linux/coredump.h | 3 ++-
include/linux/filter.h | 2 +-
include/linux/ratelimit.h | 2 +-
include/linux/sched.h | 17 ++++++++++-------
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 ++
init/init_task.c | 2 +-
ipc/sem.c | 2 +-
kernel/acct.c | 2 +-
kernel/audit.c | 4 ++--
kernel/auditsc.c | 10 +++++-----
kernel/bpf/helpers.c | 2 +-
kernel/capability.c | 4 ++--
kernel/cgroup/cgroup-v1.c | 2 +-
kernel/cred.c | 4 ++--
kernel/events/core.c | 2 +-
kernel/exit.c | 6 +++---
kernel/fork.c | 9 +++++++--
kernel/freezer.c | 4 ++--
kernel/futex/waitwake.c | 2 +-
kernel/hung_task.c | 10 +++++-----
kernel/irq/manage.c | 2 +-
kernel/kthread.c | 2 +-
kernel/locking/rtmutex.c | 2 +-
kernel/printk/printk.c | 2 +-
kernel/sched/core.c | 22 +++++++++++-----------
kernel/sched/debug.c | 4 ++--
kernel/signal.c | 6 +++---
kernel/sys.c | 6 +++---
kernel/sysctl.c | 2 +-
kernel/time/itimer.c | 4 ++--
kernel/time/posix-cpu-timers.c | 2 +-
kernel/tsacct.c | 2 +-
kernel/workqueue.c | 6 +++---
lib/dump_stack.c | 2 +-
lib/nlattr.c | 6 +++---
mm/compaction.c | 2 +-
mm/filemap.c | 4 ++--
mm/gup.c | 2 +-
mm/memfd.c | 2 +-
mm/memory-failure.c | 10 +++++-----
mm/memory.c | 2 +-
mm/mmap.c | 4 ++--
mm/oom_kill.c | 18 +++++++++---------
mm/page_alloc.c | 4 ++--
mm/util.c | 2 +-
net/core/sock.c | 2 +-
net/dns_resolver/internal.h | 2 +-
net/ipv4/raw.c | 2 +-
net/ipv4/tcp.c | 2 +-
net/socket.c | 2 +-
security/lsm_audit.c | 4 ++--
90 files changed, 184 insertions(+), 165 deletions(-)

--
2.38.1

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