linux-kernel - [PATCHv7 00/11] thread_info: use helpers to snapshot thread flags

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Date:   Wed, 17 Nov 2021 16:30:38 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        peterz@...radead.org
Cc:     benh@...nel.crashing.org, boqun.feng@...il.com, bp@...en8.de,
        catalin.marinas@....com, dvyukov@...gle.com, efuller@...hat.com,
        elver@...gle.com, ink@...assic.park.msu.ru, joey.gouly@....com,
        jonas@...thpole.se, juri.lelli@...hat.com, linux@...linux.org.uk,
        luto@...nel.org, mark.rutland@....com, mattst88@...il.com,
        michal.simek@...inx.com, mpe@...erman.id.au, npiggin@...il.com,
        paulmck@...nel.org, paulus@...ba.org, rth@...ddle.net,
        shorne@...il.com, stefan.kristiansson@...nalahti.fi,
        vincent.guittot@...aro.org, will@...nel.org
Subject: [PATCHv7 00/11]  thread_info: use helpers to snapshot thread flags

TIP folk (Peter?), I've been assuming this would go via the TIP tree. Are you
happy to pick this up nowish, or as a fixup after the next -rc1? There have
been no significant changes since v3 (aisde from the addition of the PPC fix
for v7), and this has continued to apply cleanly since then (with no conflicts
when rebasing up to v5.16-rc1).

If nothing else, it would be really nice to get the first patch (adding the
accessors) merged, so that we can convert each architecture in turn.

Usual blurb below...

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 snapshot the thread flags, with the
intent being that these should replace all plain accesses.

Since v1 [1]:
* Drop RFC
* Make read_ti_thread_flags() __always_inline
* Clarify commit messages
* Fix typo in arm64 patch
* Accumulate Reviewed-by / Acked-by tags
* Drop powerpc patch to avoid potential conflicts (per [2])

Since v2 [3]:
* Rebase to v5.14-rc1
* Reinstate powerpc patch

Since v3 [4]:
* Rebase to v5.14-rc4

Since v4 [5]:
* Rebase to v5.15-rc1
* Apply Acked-by / Tested-by tags

Since v5 [6]:
* Fix trivial whitespace bug in x86 patch

Since v6 [7]:
* Rebase to v5.16-rc1
* Fix new issue on PPC where thread flags could be discarded

[1] https://lore.kernel.org/r/20210609122001.18277-1-mark.rutland@arm.com
[2] https://lore.kernel.org/r/87k0mvtgeb.fsf@mpe.ellerman.id.au
[3] https://lore.kernel.org/r/20210621090602.16883-1-mark.rutland@arm.com
[4] https://lore.kernel.org/r/20210713113842.2106-1-mark.rutland@arm.com
[5] https://lore.kernel.org/r/20210803095428.17009-1-mark.rutland@arm.com
[6] https://lore.kernel.org/r/20210914103027.53565-1-mark.rutland@arm.com
[7] https://lore.kernel.org/lkml/20211022135643.7442-1-mark.rutland@arm.com

Thanks,
Mark.

Mark Rutland (11):
  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: snapshot thread flags
  microblaze: snapshot thread flags
  openrisc: snapshot thread flags
  powerpc: avoid discarding flags in system_call_exception()
  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/entry-common.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     | 15 +++++++--------
 arch/powerpc/kernel/ptrace/ptrace.c |  3 +--
 arch/x86/kernel/process.c           |  8 ++++----
 arch/x86/kernel/process.h           |  4 ++--
 arch/x86/mm/tlb.c                   |  2 +-
 include/linux/entry-kvm.h           |  2 +-
 include/linux/thread_info.h         | 14 ++++++++++++++
 kernel/entry/common.c               |  4 ++--
 kernel/entry/kvm.c                  |  4 ++--
 kernel/sched/core.c                 |  2 +-
 19 files changed, 46 insertions(+), 34 deletions(-)

-- 
2.11.0