Re: [PATCH 13/33] sched/isolation: Convert housekeeping cpumasks to rcu pointers

Le Sun, Jan 11, 2026 at 09:45:36PM -0500, Waiman Long a écrit :

On 1/7/26 6:56 AM, Simon Horman wrote:

quoted

On Thu, Jan 01, 2026 at 11:13:38PM +0100, Frederic Weisbecker wrote:

quoted

HK_TYPE_DOMAIN's cpumask will soon be made modifiable by cpuset.
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@kernel.org>
---
  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);
+

Hi Frederic,

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 *

...

The direct housekeeping.cpumasks[type] reference is in the newly merged
check after Federic's initial patch series.

                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.

Good catch guys! Fixing this.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs