Hi,
I have a question about a checkpatch.pl warning against the
use of NR_CPUS -
$ ./scripts/checkpatch.pl diff.patch
WARNING: usage of NR_CPUS is often wrong - consider using
cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc
#14: FILE: arch/sparc/kernel/irq_64.c:1039:
+ BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > PAGE_SIZE);
num_possible_cpus() is the hard limit on a domain without platform reboot,
it is capped by both NR_CPUS and 'max_cpus' (a platform property in the
machine description). So it is theoretically possible to have NR_CPUS>4096
but num_possible_cpus() < 4096 -- a scenario I think we'd prefer to reject.
Is it okay to ignore the checkpatch.pl warning in this case?
thanks,
-jane
On 06/04/2017 04:46 PM, David Miller wrote:
From: Jane Chu <jane.chu@xxxxxxxxxx>
Date: Thu, 1 Jun 2017 15:39:13 -0600
diff --git a/arch/sparc/kernel/irq_64.c b/arch/sparc/kernel/irq_64.c
index 4d0248a..5b19108 100644
--- a/arch/sparc/kernel/irq_64.c
+++ b/arch/sparc/kernel/irq_64.c
@@ -1034,12 +1034,12 @@ static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
{
#ifdef CONFIG_SMP
unsigned long page;
+ unsigned int order;
- BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > (PAGE_SIZE - 64));
-
- page = get_zeroed_page(GFP_KERNEL);
+ order = get_order(num_possible_cpus() * sizeof(u16) + 64);
+ page = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
if (!page) {
The only reason we allocated these two items together was because it
was convenient and it all fit into a single page.
Since it now doesn't, it makes sense to split it up.
Simply use a single page for the cpu_list_pa and kzalloc for the
cpu_mondo_block.
This also allows to keep the BUILD_BUG_ON(), which I really wish
you hadn't tried to remove.
static void __init init_cpu_send_mondo_info(struct trap_per_cpu *tb)
{
#ifdef CONFIG_SMP
unsigned long page;
void *mondo;
BUILD_BUG_ON((NR_CPUS * sizeof(u16)) > PAGE_SIZE);
mondo = kzalloc(64, GFP_KERNEL);
if (!mondo) {
prom_printf("SUN4V: Error, cannot allocate mondo block.\n");
prom_halt();
}
tb->cpu_mondo_block_pa = __pa(mondo);
page = get_zeroed_page(GFP_KERNEL);
if (!page) {
prom_printf("SUN4V: Error, cannot allocate cpu list page.\n");
prom_halt();
}
tb->cpu_list_pa = __pa(page);
#endif
}
Thanks.
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