* Use case
When debugging and tracing complex programs with hundreds of threads, 16 bytes
long thread names are not enough anymore. cmd_line can show a lot of
characters, but it's not affected by pthread_setname_np() or
prctl(PR_SET_NAME), so let's give the same love kthreads got with commit
6b59808bfe48 ("workqueue: Show the latest workqueue name in
/proc/PID/{comm,stat,status}"). This patchset creates a new
PR_{SET,GET}_EXT_NAME that supports 64 bytes long names.
It also introduces a new function copy_task_comm() that ensures that the string
is always NUL-terminated despite of mismatching sizes of buffers. We can't just
use strscpy() because it proved to give some overhead [0] in tracing.
* Patchset
Patch 1 and 2 do some prep work in order to avoid buffer overflows around
the kernel, now that current->comm is bigger. It also make sure that if
the destination buffer is smaller than TASK_COMM_EXT_LEN, it will
be NUL-terminated.
Patch 3 adds a KUnit for the new function copy_task_comm()
Patch 4 sets current->comm length to TASK_COMM_EXT_LEN and take care of
making sure that current userspace APIs gets only TASK_COMM_LEN.
Patch 5 creates new prctl() to set and get all the TASK_COMM_EXT_LEN bytes.
Patch 6 adapts the existing selftest for this new interface.
* Testing
selftests/prctl/set-process-name.c survives this patchset, and it was extended
to the new interface. KUnit test was modified to support copy_task_comm().
I ran the same benchmark as at [0], and no significant change was found.
* Changes
Since v3:
- Simplify Get rid of get_task_comm() commit
- Simplify copy_task_comm(): just do a memcpy + NUL char at the end
- Link to v3: https://patch.msgid.link/20260612-tonyk-long_name-v3-0-7989b66e8a99@igalia.com
Since v2:
- Add a custom function copy_task_comm() that uses memcpy when possible and
fallback to strscpy(). It always ensures that the string in NUL-terminated
- Add KUnit test for the new function
- Link to v2: https://patch.msgid.link/20260524-tonyk-long_name-v2-0-332f6bd041c4@igalia.com
Since v1:
- Replace new strtostr() with strscpy()
- Don't replace memcpy in tools/
- Link to v1: https://patch.msgid.link/20260517-tonyk-long_name-v1-0-3c282eaa91e2@igalia.com
[0] https://lore.kernel.org/lkml/20260526190625.3f4aca0a@gandalf.local.home/
---
André Almeida (6):
treewide: Get rid of get_task_comm()
treewide: Replace memcpy(..., current->comm) with copy_task_comm()
lib/string_kunit: Add test for copy_task_comm()
sched: Extend task command name with TASK_COMM_EXT_LEN
prctl: Add support for long user thread names
selftests: prctl: Add test for long thread names
drivers/connector/cn_proc.c | 2 +-
drivers/dma-buf/sw_sync.c | 2 +-
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_fence.c | 2 +-
drivers/gpu/drm/amd/amdgpu/amdgpu_eviction_fence.c | 2 +-
drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c | 2 +-
drivers/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/panthor/panthor_sched.c | 2 +-
drivers/gpu/drm/virtio/virtgpu_ioctl.c | 2 +-
drivers/hwtracing/stm/core.c | 2 +-
drivers/tty/tty_audit.c | 2 +-
fs/binfmt_elf.c | 2 +-
fs/binfmt_elf_fdpic.c | 2 +-
fs/proc/array.c | 2 +-
include/linux/coredump.h | 2 +-
include/linux/sched.h | 29 +++++++----------
include/linux/tracepoint.h | 4 +--
include/trace/events/block.h | 10 +++---
include/trace/events/coredump.h | 2 +-
include/trace/events/f2fs.h | 4 +--
include/trace/events/oom.h | 2 +-
include/trace/events/osnoise.h | 2 +-
include/trace/events/sched.h | 10 +++---
include/trace/events/signal.h | 2 +-
include/trace/events/task.h | 7 ++--
include/uapi/linux/prctl.h | 3 ++
kernel/audit.c | 6 ++--
kernel/auditsc.c | 6 ++--
kernel/printk/nbcon.c | 2 +-
kernel/printk/printk.c | 4 +--
kernel/sys.c | 23 ++++++++++---
lib/tests/string_kunit.c | 38 ++++++++++++++++++++++
net/bluetooth/hci_sock.c | 2 +-
net/netfilter/nf_tables_api.c | 4 ++-
security/integrity/integrity_audit.c | 3 +-
security/ipe/audit.c | 3 +-
security/landlock/domain.c | 2 +-
security/lsm_audit.c | 7 ++--
tools/testing/selftests/prctl/set-process-name.c | 36 ++++++++++++++++++++
43 files changed, 172 insertions(+), 79 deletions(-)
---
base-commit: 481ed5dd3ed7136f627b8ec372ba39f5b2e7d27f
change-id: 20260516-tonyk-long_name-b9f345aeb041
Best regards,
--
André Almeida <andrealmeid@igalia.com>