[PATCH v3 2/2] x86: Fix /proc/cpuinfo cpumask warning

Andrew Jones
2022-10-14T15:58:54Z

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@ventanamicro.com>
Cc: Yury Norov <yury.norov@gmail.com>
---
arch/x86/kernel/cpu/proc.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index 099b6f0d96bd..de3f93ac6e49 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -153,6 +153,9 @@ static int show_cpuinfo(struct seq_file *m, void *v)

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 &cpu_data(*pos);
--
2.37.3