Re: [PATCH 13/33] sched/isolation: Convert housekeeping cpumasks to rcu pointers
From: Waiman Long
Date: Sun Jan 11 2026 - 21:45:55 EST
On 1/7/26 6:56 AM, Simon Horman wrote:
On Thu, Jan 01, 2026 at 11:13:38PM +0100, Frederic Weisbecker wrote:The direct housekeeping.cpumasks[type] reference is in the newly merged check after Federic's initial patch series.
HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.Hi Frederic,
A synchronization mechanism is then needed to synchronize the updates
with the housekeeping cpumask readers.
Turn the housekeeping cpumasks into RCU pointers. Once a housekeeping
cpumask will be modified, the update side will wait for an RCU grace
period and propagate the change to interested subsystem when deemed
necessary.
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
kernel/sched/isolation.c | 58 +++++++++++++++++++++++++---------------
kernel/sched/sched.h | 1 +
2 files changed, 37 insertions(+), 22 deletions(-)
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 11a623fa6320..83be49ec2b06 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -21,7 +21,7 @@ DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
EXPORT_SYMBOL_GPL(housekeeping_overridden);
struct housekeeping {
- cpumask_var_t cpumasks[HK_TYPE_MAX];
+ struct cpumask __rcu *cpumasks[HK_TYPE_MAX];
unsigned long flags;
};
@@ -33,17 +33,28 @@ bool housekeeping_enabled(enum hk_type type)
}
EXPORT_SYMBOL_GPL(housekeeping_enabled);
+const struct cpumask *housekeeping_cpumask(enum hk_type type)
+{
+ if (static_branch_unlikely(&housekeeping_overridden)) {
+ if (housekeeping.flags & BIT(type)) {
+ return rcu_dereference_check(housekeeping.cpumasks[type], 1);
+ }
+ }
+ return cpu_possible_mask;
+}
+EXPORT_SYMBOL_GPL(housekeeping_cpumask);
+
I think this patch should also update the access to housekeeping.cpumasks
in housekeeping_setup(), on line 200, to use housekeeping_cpumask().
As is, sparse flags __rcu a annotation miss match there.
kernel/sched/isolation.c:200:80: warning: incorrect type in argument 3 (different address spaces)
kernel/sched/isolation.c:200:80: expected struct cpumask const *srcp3
kernel/sched/isolation.c:200:80: got struct cpumask [noderef] __rcu *
...
iter_flags = housekeeping.flags & (HK_FLAG_KERNEL_NOISE | HK_FLAG_DOMAIN);
type = find_first_bit(&iter_flags, HK_TYPE_MAX);
/*
* Pass the check if none of these flags were previously set or
* are not in the current selection.
*/
iter_flags = flags & (HK_FLAG_KERNEL_NOISE | HK_FLAG_DOMAIN);
first_cpu = (type == HK_TYPE_MAX || !iter_flags) ? 0 :
cpumask_first_and_and(cpu_present_mask,
housekeeping_staging, housekeeping.cpumasks[type]);
Maybe that is why it is missed.
Cheers,
Longman