Merge branch 'implement-mechanism-to-signal-other-threads'

Merge branch 'implement-mechanism-to-signal-other-threads'

Puranjay Mohan says:

====================
Implement mechanism to signal other threads

This set implements a kfunc called bpf_send_signal_task() that is similar
to sigqueue() as it can send a signal along with a cookie to a thread or
thread group.

The send_signal selftest has been updated to also test this new kfunc under
all contexts.

Changes in v5:
v4: https://lore.kernel.org/all/20241008114940.44305-1-puranjay@kernel.org/
- Call copy_siginfo() only if work->has_siginfo is true in
  bpf_send_signal_common()
- Add Acked-by: Andrii Nakryiko <andrii@kernel.org>

Changes in v4:
v3: https://lore.kernel.org/all/20241007103426.128923-1-puranjay@kernel.org/
- Fix the selftest to make it work for big-endian archs.
- Fix a build warning on 32-bit archs.
- Some style changes and code refactors suggested by Andrii

Changes in v3:
v2: https://lore.kernel.org/all/20240926115328.105634-1-puranjay@kernel.org/
- make the cookie u64 instead of int.
- re use code from bpf_send_signal_common

Changes in v2:
v1: https://lore.kernel.org/bpf/20240724113944.75977-1-puranjay@kernel.org/
- Convert to a kfunc
- Add mechanism to send a cookie with the signal.
====================

Link: https://lore.kernel.org/r/20241016084136.10305-1-puranjay@kernel.org
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>