linux-kernel - [PATCH v3 0/2] Fix /proc/cpuinfo cpumask warning

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Message-Id: <20221014155845.1986223-1-ajones@ventanamicro.com>
Date:   Fri, 14 Oct 2022 17:58:43 +0200
From:   Andrew Jones <ajones@...tanamicro.com>
To:     x86@...nel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Yury Norov <yury.norov@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        openrisc@...ts.librecores.org,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Subject: [PATCH v3 0/2] Fix /proc/cpuinfo cpumask warning

Commit 78e5a3399421 ("cpumask: fix checking valid cpu range") has
started issuing warnings[*] when cpu indices equal to nr_cpu_ids - 1
are passed to cpumask_next* functions. seq_read_iter() and cpuinfo's
start and next seq operations implement a pattern like

  n = cpumask_next(n - 1, mask);
  show(n);
  while (1) {
      ++n;
      n = cpumask_next(n - 1, mask);
      if (n >= nr_cpu_ids)
          break;
      show(n);
  }

which will issue the warning when reading /proc/cpuinfo.

[*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled.

This series address the issue for x86 and riscv, but from a quick
grep of cpuinfo seq operations, I think at least openrisc, powerpc,
and s390 also need an equivalent patch. While the test is simple (see
next paragraph) I'm not equipped to test on each architecture.

To test, just build a kernel with DEBUG_PER_CPU_MAPS enabled, boot to
a shell, do 'cat /proc/cpuinfo', and look for a kernel warning.

While the patches are being posted together in a series since they're
for two different architectures they don't necessarily need to go
through the same tree.

v3:
  - Change condition from >= to == in order to still get a warning
    for > as that's unexpected. [Yury]
  - Picked up tags on the riscv patch

v2:
  - Added all the information I should have in the first place
    to the commit message [Boris]
  - Changed style of fix [Boris]

Andrew Jones (2):
  RISC-V: Fix /proc/cpuinfo cpumask warning
  x86: Fix /proc/cpuinfo cpumask warning

 arch/riscv/kernel/cpu.c    | 3 +++
 arch/x86/kernel/cpu/proc.c | 3 +++
 2 files changed, 6 insertions(+)

-- 
2.37.3