[PATCH net-next v2 0/3] Threads support in proc connector

From: Anjali Kulkarni
Date: Tue Oct 15 2024 - 13:31:08 EST


Recently we committed a fix to allow processes to receive notifications for
non-zero exits via the process connector module. Commit is a4c9a56e6a2c.

However, for threads, when it does a pthread_exit(&exit_status) call, the
kernel is not aware of the exit status with which pthread_exit is called.
It is sent by child thread to the parent process, if it is waiting in
pthread_join(). Hence, for a thread exiting abnormally, kernel cannot
send notifications to any listening processes.

The exception to this is if the thread is sent a signal which it has not
handled, and dies along with it's process as a result; for eg. SIGSEGV or
SIGKILL. In this case, kernel is aware of the non-zero exit and sends a
notification for it.

For our use case, we cannot have parent wait in pthread_join, one of the
main reasons for this being that we do not want to track normal
pthread_exit(), which could be a very large number. We only want to be
notified of any abnormal exits. Hence, threads are created with
pthread_attr_t set to PTHREAD_CREATE_DETACHED.

To fix this problem, we add a new type PROC_CN_MCAST_NOTIFY to proc connector
API, which allows a thread to send it's exit status to kernel either when
it needs to call pthread_exit() with non-zero value to indicate some
error or from signal handler before pthread_exit().

v1->v2 changes:
- Handled comment by Peter Zijlstra to remove locking for PF_EXIT_NOTIFY
task->flags.
- Added error handling in thread.c

v->v1 changes:
- Handled comment by Simon Horman to remove unused err in cn_proc.c
- Handled comment by Simon Horman to make adata and key_display static
in cn_hash_test.c

Anjali Kulkarni (3):
connector/cn_proc: Add hash table for threads
connector/cn_proc: Kunit tests for threads hash table
connector/cn_proc: Selftest for threads

drivers/connector/Makefile | 2 +-
drivers/connector/cn_hash.c | 240 ++++++++++++++++++
drivers/connector/cn_proc.c | 55 +++-
drivers/connector/connector.c | 96 ++++++-
include/linux/connector.h | 47 ++++
include/linux/sched.h | 2 +-
include/uapi/linux/cn_proc.h | 4 +-
lib/Kconfig.debug | 17 ++
lib/Makefile | 1 +
lib/cn_hash_test.c | 167 ++++++++++++
lib/cn_hash_test.h | 12 +
tools/testing/selftests/connector/Makefile | 23 +-
.../testing/selftests/connector/proc_filter.c | 5 +
tools/testing/selftests/connector/thread.c | 116 +++++++++
.../selftests/connector/thread_filter.c | 96 +++++++
15 files changed, 873 insertions(+), 10 deletions(-)
create mode 100644 drivers/connector/cn_hash.c
create mode 100644 lib/cn_hash_test.c
create mode 100644 lib/cn_hash_test.h
create mode 100644 tools/testing/selftests/connector/thread.c
create mode 100644 tools/testing/selftests/connector/thread_filter.c

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2.46.0