[PATCH v3 0/9] preempt: Add a generic function to return the preemption string.

[Sebastian Andrzej Siewior]

The individual architectures often add the preemption model to the begin
of the backtrace. This is the case on X86 or ARM64 for the "die" case
but not for regular warning. With the addition of DYNAMIC_PREEMPT for
PREEMPT_RT we end up with CONFIG_PREEMPT and CONFIG_PREEMPT_RT set
simultaneously. That means that everyone who tried to add that piece of
information gets it wrong for PREEMPT_RT because PREEMPT is checked
first.

This series adds a generic helper which is used by
dump_stack_print_info() and other architectures which don't use the
function and provide this information on their own.

I collected ACKs for all architectures but x86.

v2…v3 https://lore.kernel.org/all/20250203141632.440554-1-bigeasy@xxxxxxxxxxxxx/
  - powerpc/ s390 and xtensa had the preemption string twice. Removed
    from the arch code.
  - Keeping the same printk() invocation, avoiding adding any level.
  - #1 has now a table showing which strings are possible.

RFC…v2 https://lore.kernel.org/all/20241206113431.Q-VXMlru@xxxxxxxxxxxxx/
  - Split into individual patches.
  - Implement preempt_model_str() based on feedback by Peter Zijlstra
    and Steven Rostedt.

Sebastian Andrzej Siewior (9):
  sched: Add a generic function to return the preemption string.
  lib/dump_stack: Use preempt_model_str().
  arm: Rely on generic printing of preemption model.
  arm64: Rely on generic printing of preemption model.
  powerpc: Rely on generic printing of preemption model.
  s390: Rely on generic printing of preemption model.
  x86: Rely on generic printing of preemption model.
  xtensa: Rely on generic printing of preemption model.
  tracing: Use preempt_model_str().

 arch/arm/kernel/traps.c      | 11 ++-------
 arch/arm64/kernel/traps.c    | 10 +-------
 arch/powerpc/kernel/traps.c  |  3 +--
 arch/s390/kernel/dumpstack.c |  7 +-----
 arch/x86/kernel/dumpstack.c  |  9 ++-----
 arch/xtensa/kernel/traps.c   |  6 +----
 include/linux/preempt.h      |  2 ++
 kernel/sched/core.c          | 47 ++++++++++++++++++++++++++++++++++++
 kernel/sched/debug.c         | 10 +++++---
 kernel/sched/sched.h         |  1 +
 kernel/trace/trace.c         |  7 +-----
 lib/dump_stack.c             |  4 +--
 12 files changed, 67 insertions(+), 50 deletions(-)

Sebastian