binfmt_elf, coredump: Log the reason of the failed core dumps

A powerful way to diagnose crashes is to analyze the core dump produced upon the failure. Missing or malformed core dump files hinder these investigations. I'd like to propose changes that add logging as to why the kernel would not finish writing out the core dump file.

To help in diagnosing the user mode helper not writing out the entire coredump contents, the changes also log short statistics on the dump collection. I'd advocate for keeping this at the info level on these grounds.

For validation, I built the kernel and a simple user space to exercize the new code.

[V3]
- Standartized the existing logging to report TGID and comm consistently
- Fixed compiler warnings for the 32-bit systems (used %zd in the format strings)

[V2]
https://lore.kernel.org/all/[email protected]/
- Used _ratelimited to avoid spamming the system log
- Added comm and PID to the log messages
- Added logging to the failure paths in dump_interrupted, dump_skip, and dump_emit
- Fixed compiler warnings produced when CONFIG_COREDUMP is disabled

[V1]
https://lore.kernel.org/all/[email protected]/

Roman Kisel (2):
coredump: Standartize and fix logging
binfmt_elf, coredump: Log the reason of the failed core dumps

 fs/binfmt_elf.c          |  48 +++++++++----
 fs/coredump.c            | 150 +++++++++++++++++++++++++++------------
 include/linux/coredump.h |  30 +++++++-
 kernel/signal.c          |  21 +++++-
 4 files changed, 188 insertions(+), 61 deletions(-)

base-commit: 831bcbcead6668ebf20b64fdb27518f1362ace3a

2.45.2