[PATCH v5 00/10] thread_info: use helpers to snapshot thread flags

From: Mark Rutland
Date: Tue Sep 14 2021 - 06:30:40 EST


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've been assuming this would go via the TIP tree. TIP folk, are you happy to
pick this up, or would you be happy to pick at least the first three patches
which cover the core bits?

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

[1] https://lore.kernel.org/r/20210609122001.18277-1-mark.rutland@xxxxxxx
[2] https://lore.kernel.org/r/87k0mvtgeb.fsf@xxxxxxxxxxxxxxxxxx
[3] https://lore.kernel.org/r/20210621090602.16883-1-mark.rutland@xxxxxxx
[4] https://lore.kernel.org/r/20210713113842.2106-1-mark.rutland@xxxxxxx
[5] https://lore.kernel.org/r/20210803095428.17009-1-mark.rutland@xxxxxxx

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: snapshot 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/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 | 13 ++++++-------
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 | 14 ++++++++++++++
kernel/entry/common.c | 4 ++--
kernel/entry/kvm.c | 4 ++--
kernel/sched/core.c | 2 +-
19 files changed, 46 insertions(+), 34 deletions(-)

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2.11.0