linux-kernel - [PATCH v2 0/4] cpumask: Fix invalid uniprocessor assumptions

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Date:   Sat,  4 Jun 2022 19:15:55 +0200
From:   Sander Vanheule <sander@...nheule.net>
To:     Peter Zijlstra <peterz@...radead.org>,
        Yury Norov <yury.norov@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Valentin Schneider <vschneid@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marco Elver <elver@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Sander Vanheule <sander@...nheule.net>
Subject: [PATCH v2 0/4] cpumask: Fix invalid uniprocessor assumptions

On uniprocessor builds, it is currently assumed that any cpumask will
contain the single CPU: cpu0. This assumption is used to provide
optimised implementations.

The current assumption also appears to be wrong, by ignoring the fact
that users can provide empty cpumask-s. This can result in bugs as
explained in [1].

This series introduces some basic tests, and updates the optimisations
for uniprocessor builds.

[1] https://lore.kernel.org/all/20220530082552.46113-1-sander@svanheule.net/

Changes since v1:
Link: https://lore.kernel.org/all/cover.1654201862.git.sander@svanheule.net/
  - Place tests in lib/test_cpumask.c
  - Drop the modified UP code in favor of the generic SMP implementation
  - Update declaration of cpumask_next_wrap()

Sander Vanheule (4):
  lib/test: Introduce cpumask KUnit test suite
  cpumask: Fix invalid uniprocessor mask assumption
  cpumask: Add UP optimised for_each_*_cpu versions
  cpumask: Update cpumask_next_wrap() signature

 include/linux/cpumask.h |  89 +++----------------------------
 lib/Kconfig.debug       |   9 ++++
 lib/Makefile            |   4 +-
 lib/test_cpumask.c      | 115 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 134 insertions(+), 83 deletions(-)
 create mode 100644 lib/test_cpumask.c

-- 
2.36.1