linux-kernel - [RFC PATCH 00/10] thread_info: use helpers to snapshot thread flags

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Date:   Wed,  9 Jun 2021 13:19:51 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, boqun.feng@...il.com, bp@...en8.de,
        catalin.marinas@....com, dvyukov@...gle.com, elver@...gle.com,
        ink@...assic.park.msu.ru, jonas@...thpole.se,
        juri.lelli@...hat.com, linux@...linux.org.uk, luto@...nel.org,
        mark.rutland@....com, mattst88@...il.com, mingo@...hat.com,
        monstr@...str.eu, mpe@...erman.id.au, paulmck@...nel.org,
        paulus@...ba.org, peterz@...radead.org, rth@...ddle.net,
        shorne@...il.com, stefan.kristiansson@...nalahti.fi,
        tglx@...utronix.de, vincent.guittot@...aro.org, will@...nel.org
Subject: [RFC PATCH 00/10] thread_info: use helpers to snapshot thread flags

As thread_info::flags scan be manipulated by remote threads, it is necessary to
use atomics or READ_ONCE() to ensure that code manipulates a consistent
snapshot, but we open-code plain accesses to thread_info::flags across the kernel tree.

Generally we get away with this, but tools like KCSAN legitimately warn that
there is a data-race, and this is potentially fragile with compiler
optimizations, LTO, etc.

These patches introduce new helpers to snahpshot the thread flags, with the
intent being that these should replace all plain accesses.

I'm sending this as an RFC as I'm certain I've missed places that need to be
moved over to the helpers, and I want to check that this has the right shape
before digging deeper.

Thanks,
Mark.

Mark Rutland (10):
  thread_info: add helpers to snapshot thread flags
  entry: snapshot thread flags
  sched: snapshot thread flags
  alpha: snapshot thread flags
  arm: snapshot thread flags
  arm64: read thread flags
  microblaze: snapshot thread flags
  openrisc: snapshot thread flags
  powerpc: snapshot thread flags
  x86: snapshot thread flags

 arch/alpha/kernel/signal.c          |  2 +-
 arch/arm/kernel/signal.c            |  2 +-
 arch/arm/mm/alignment.c             |  2 +-
 arch/arm64/kernel/ptrace.c          |  4 ++--
 arch/arm64/kernel/signal.c          |  2 +-
 arch/arm64/kernel/syscall.c         |  4 ++--
 arch/microblaze/kernel/signal.c     |  2 +-
 arch/openrisc/kernel/signal.c       |  2 +-
 arch/powerpc/kernel/interrupt.c     | 16 ++++++++--------
 arch/powerpc/kernel/ptrace/ptrace.c |  3 +--
 arch/x86/kernel/process.c           |  8 ++++----
 arch/x86/kernel/process.h           |  6 +++---
 arch/x86/mm/tlb.c                   |  2 +-
 include/linux/entry-kvm.h           |  2 +-
 include/linux/thread_info.h         | 10 ++++++++++
 kernel/entry/common.c               |  4 ++--
 kernel/entry/kvm.c                  |  4 ++--
 kernel/sched/core.c                 |  2 +-
 18 files changed, 43 insertions(+), 34 deletions(-)

-- 
2.11.0