[PATCH v2] RISC-V: Fix /proc/cpuinfo cpumask warning

From: Andrew Jones
Date: Wed Oct 12 2022 - 04:29:59 EST


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@xxxxxxxxxxxxxxxx>
Cc: Yury Norov <yury.norov@xxxxxxxxx>
---
v2:
- Got comments on the x86 equivalent patch and made the same
changes to this one
- Added all the information I should have in the first place
to the commit message [Boris]
- Changed style of fix [Boris]


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 4aa8cd749441..63138b880b92 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