[PATCH v2 00/11] powerpc: KCSAN fix warnings and mark accesses

Rohan McLure rmclure at linux.ibm.com
Wed May 10 13:31:06 AEST 2023

v1 of this patch series available here:
Link: https://lore.kernel.org/linuxppc-dev/20230508020120.218494-1-rmclure@linux.ibm.com/

The KCSAN sanitiser notifies programmers of instances where unmarked
accesses to shared state has lead to a data race, or when the compiler
has liberty to reorder an unmarked access and so generate a data race.
This patch series deals with benign data races, which nonetheless need
annotation in order to ensure the correctness of the emitted code.

In keeping with the principles given in
tools/memory-model/Documentation/access-marking.txt, racing reads of
shared state for purely diagnostic/debug purposes are annotated with
data_race, while reads/writes that are examples of intention polling of
shared variables are performed with READ_ONCE, WRITE_ONCE.

These changes remove the majority of warnings observable on pseries and
powernv, where for development, I was able to narrow down to only power
relevant bugs by temporarily disabling sanitisation for all other files.
Future patch series will deal with the subtler bugs which persist under
this configuration.

KCSAN races addressed:
 - qspinlock: assignign of qnode->locked and polling
 - check_return_regs_valid [h]srr_valid
 - arch_cpu_idle idle callback
 - powernv idle_state paca entry (polling the bit-lock is viewed by
   KCSAN as asynchronous access to the fields it protects)
 - Asynchronous access to irq_data->hwirq
 - Opal asynchronous event handling
 - IPIs

Miscellaneous other changes:

 - Annotate the asm-generic/mmiowb code, which riscv and powerpc each
 - Update usages of qnode->locked in powerpc's qspinlock interpretation
   to reflect the comment beside this field

 - Match READ_ONCE with WRITE_ONCE and vice versa where required
 - In arch/powerpc/lib/qspinlock.c, use kcsan_release() to notify KCSAN
   of locked being assigned prior to publish, and remove extraneous
   compiler barrier (publish_tail_cpu features memory clobber).
 - Keep polarity for locked variable in qspinlock
 - Remove extraneous READ_ONCE in mmiowb()
 - Use data_race() for power_save callback to remove instrumentation, as
   there is no real data race

Rohan McLure (11):
  powerpc: qspinlock: Mark accesses to qnode lock checks
  powerpc: qspinlock: Enforce qnode writes prior to publishing to queue
  asm-generic/mmiowb: Mark accesses to fix KCSAN warnings
  powerpc: Mark [h]ssr_valid accesses in check_return_regs_valid
  powerpc: Mark accesses to power_save callback in arch_cpu_idle
  powerpc: powernv: Fix KCSAN datarace warnings on idle_state contention
  powerpc: Annotate accesses to ipi message flags
  powerpc: Mark writes registering ipi to host cpu through kvm and
  powerpc: powernv: Annotate data races in opal events
  powerpc: powernv: Annotate asynchronous access to opal tokens
  powerpc: Mark asynchronous accesses to irq_data

 arch/powerpc/include/asm/kvm_ppc.h            |  4 ++--
 arch/powerpc/include/asm/paca.h               |  1 +
 arch/powerpc/include/asm/ptrace.h             |  4 ++--
 arch/powerpc/kernel/idle.c                    |  9 ++++++---
 arch/powerpc/kernel/interrupt.c               | 14 ++++++--------
 arch/powerpc/kernel/irq.c                     |  2 +-
 arch/powerpc/kernel/smp.c                     |  4 ++--
 arch/powerpc/kvm/book3s_hv_builtin.c          |  4 ++--
 arch/powerpc/lib/qspinlock.c                  | 11 +++++++++--
 arch/powerpc/platforms/powernv/idle.c         | 16 +++++++++-------
 arch/powerpc/platforms/powernv/opal-async.c   |  6 +++---
 arch/powerpc/platforms/powernv/opal-irqchip.c |  6 +++---
 arch/powerpc/platforms/powernv/pci-ioda.c     | 12 ++++++------
 include/asm-generic/mmiowb.h                  | 14 +++++++++-----
 include/linux/irq.h                           |  2 +-
 kernel/irq/irqdomain.c                        |  4 ++--
 16 files changed, 64 insertions(+), 49 deletions(-)


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