linux-kernel - [PATCH v3 1/2] RISC-V: Fix /proc/cpuinfo cpumask warning

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Message-Id: <20221014155845.1986223-2-ajones@ventanamicro.com>
Date:   Fri, 14 Oct 2022 17:58:44 +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, Anup Patel <anup@...infault.org>,
        Conor Dooley <conor.dooley@...rochip.com>
Subject: [PATCH v3 1/2] RISC-V: 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. Ensure no
warning is generated by validating the cpu index before calling
cpumask_next().

[*] Warnings will only appear with DEBUG_PER_CPU_MAPS enabled.

Signed-off-by: Andrew Jones <ajones@...tanamicro.com>
Cc: Yury Norov <yury.norov@...il.com>
Reviewed-by: Anup Patel <anup@...infault.org>
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
Tested-by: Conor Dooley <conor.dooley@...rochip.com>
---
 arch/riscv/kernel/cpu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index 4d0dece5996c..5aa0ae8dd115 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -166,6 +166,9 @@ static void print_mmu(struct seq_file *f)
 
 static void *c_start(struct seq_file *m, loff_t *pos)
 {
+	if (*pos == nr_cpu_ids)
+		return NULL;
+
 	*pos = cpumask_next(*pos - 1, cpu_online_mask);
 	if ((*pos) < nr_cpu_ids)
 		return (void *)(uintptr_t)(1 + *pos);
-- 
2.37.3