[patch V4 00/12] rseq: Implement time slice extension mechanism

[Thomas Gleixner <tglx@linutronix.de>]

This is a follow up on the V3 version:

     https://lore.kernel.org/20251029125514.496134233@linutronix.de

V1 contains a detailed explanation:

     https://lore.kernel.org/20250908225709.144709889@linutronix.de

TLDR: Time slice extensions are an attempt to provide opportunistic
priority ceiling without the overhead of an actual priority ceiling
protocol, but also without the guarantees such a protocol provides.

The intent is to avoid situations where a user space thread is interrupted
in a critical section and scheduled out, while holding a resource on which
the preempting thread or other threads in the system might block on. That
obviously prevents those threads from making progress in the worst case for
at least a full time slice. Especially in the context of user space
spinlocks, which are a patently bad idea to begin with, but that's also
true for other mechanisms.

This series uses the existing RSEQ user memory to implement it.

Changes vs. V3:

   - Rebase on the newest uaccess, RSEQ and CID changes

   - Make the example code correct - Prakash

   - Update comment - Steven

   - Finally get the __setup() nonsense right - Randy

   - Picked up Reviewed/Acked-by tags where appropriate

The CID modifications on which this series is based on can be found here:

    https://lore.kernel.org/20251104075053.700034556@linutronix.de

and in git:

    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rseq/cid

For your convenience all of it is also available as a conglomerate from
git:

    git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git rseq/slice

Thanks,

	tglx
---
 Documentation/admin-guide/kernel-parameters.txt |    5 
 Documentation/admin-guide/sysctl/kernel.rst     |    6 
 Documentation/userspace-api/index.rst           |    1 
 Documentation/userspace-api/rseq.rst            |  119 +++++++++
 arch/alpha/kernel/syscalls/syscall.tbl          |    1 
 arch/arm/tools/syscall.tbl                      |    1 
 arch/arm64/tools/syscall_32.tbl                 |    1 
 arch/m68k/kernel/syscalls/syscall.tbl           |    1 
 arch/microblaze/kernel/syscalls/syscall.tbl     |    1 
 arch/mips/kernel/syscalls/syscall_n32.tbl       |    1 
 arch/mips/kernel/syscalls/syscall_n64.tbl       |    1 
 arch/mips/kernel/syscalls/syscall_o32.tbl       |    1 
 arch/parisc/kernel/syscalls/syscall.tbl         |    1 
 arch/powerpc/kernel/syscalls/syscall.tbl        |    1 
 arch/s390/kernel/syscalls/syscall.tbl           |    1 
 arch/s390/mm/pfault.c                           |    3 
 arch/sh/kernel/syscalls/syscall.tbl             |    1 
 arch/sparc/kernel/syscalls/syscall.tbl          |    1 
 arch/x86/entry/syscalls/syscall_32.tbl          |    1 
 arch/x86/entry/syscalls/syscall_64.tbl          |    1 
 arch/xtensa/kernel/syscalls/syscall.tbl         |    1 
 include/linux/entry-common.h                    |    2 
 include/linux/rseq.h                            |   11 
 include/linux/rseq_entry.h                      |  191 ++++++++++++++-
 include/linux/rseq_types.h                      |   30 ++
 include/linux/sched.h                           |    7 
 include/linux/syscalls.h                        |    1 
 include/linux/thread_info.h                     |   16 -
 include/uapi/asm-generic/unistd.h               |    5 
 include/uapi/linux/prctl.h                      |   10 
 include/uapi/linux/rseq.h                       |   38 +++
 init/Kconfig                                    |   12 
 kernel/entry/common.c                           |   14 -
 kernel/entry/syscall-common.c                   |   11 
 kernel/rcu/tiny.c                               |    8 
 kernel/rcu/tree.c                               |   14 -
 kernel/rcu/tree_exp.h                           |    3 
 kernel/rcu/tree_plugin.h                        |    9 
 kernel/rcu/tree_stall.h                         |    3 
 kernel/rseq.c                                   |  299 ++++++++++++++++++++++++
 kernel/sys.c                                    |    6 
 kernel/sys_ni.c                                 |    1 
 scripts/syscall.tbl                             |    1 
 tools/testing/selftests/rseq/.gitignore         |    1 
 tools/testing/selftests/rseq/Makefile           |    5 
 tools/testing/selftests/rseq/rseq-abi.h         |   27 ++
 tools/testing/selftests/rseq/slice_test.c       |  198 +++++++++++++++
 47 files changed, 1020 insertions(+), 53 deletions(-)