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().

We also need to filter packets with non-zero exit notifications futher
based on instances, which can be identified by task names. Hence, added a
comm field to the packet's struct proc_event, in which task->comm is
stored.

v2->v3 changes:
- Handled comment by Liam Howlett to set hdev to NULL and add comment on
  it
- Handled comment by Liam Howlett to combine functions for deleting+get
  and deleting into one.
- Handled comment by Liam Howlett to remove extern in the functions
  defined in cn_hash_test.h
- Some nits by Liam Howlett fixed.
- Made threads.c automated, by having an exit.log file created by
  proc_filter.c, which threads.c checks to see if the values reported
  for thread exits are correct. This was for a comment by Liam Howlett to
  make the tests automated.
- Added "comm" field to struct proc_event, to copy the task's name to
  the packet to allow further filtering by packets.
 
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                   | 221 ++++++++++++++++++
 drivers/connector/cn_proc.c                   |  62 ++++-
 drivers/connector/connector.c                 |  75 +++++-
 include/linux/connector.h                     |  35 +++
 include/linux/sched.h                         |   2 +-
 include/uapi/linux/cn_proc.h                  |   5 +-
 lib/Kconfig.debug                             |  17 ++
 lib/Makefile                                  |   1 +
 lib/cn_hash_test.c                            | 167 +++++++++++++
 lib/cn_hash_test.h                            |  10 +
 tools/testing/selftests/connector/Makefile    |  23 +-
 .../testing/selftests/connector/proc_filter.c |  34 ++-
 tools/testing/selftests/connector/thread.c    | 202 ++++++++++++++++
 .../selftests/connector/thread_filter.c       |  96 ++++++++
 15 files changed, 937 insertions(+), 15 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