[PATCH 1/5] cgroup/cpuset: Don't call validate_change() for some flag changes

Waiman Long
2021-06-03T21:25:01Z

The update_flag() is called with one flag bit change and without change
in the various cpumasks in the cpuset. Moreover, not all changes in the
flag bits are validated in validate_change(). In particular, the load
balance flag and the two spread flags are not checked there. So there
is no point in calling validate_change() if those flag bits change.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cpuset.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index adb5190c4429..65ad6995ad77 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1891,7 +1891,7 @@ static void update_tasks_flags(struct cpuset *cs)
* cs: the cpuset to update
* turning_on: whether the flag is being set or cleared
*
- * Call with cpuset_mutex held.
+ * Call with cpuset_mutex held & cpumasks remain unchanged.
*/

static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
@@ -1911,16 +1911,22 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
else
clear_bit(bit, &trialcs->flags);

- err = validate_change(cs, trialcs);
- if (err < 0)
- goto out;
-
balance_flag_changed = (is_sched_load_balance(cs) !=
is_sched_load_balance(trialcs));

spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
|| (is_spread_page(cs) != is_spread_page(trialcs)));

+ /*
+ * validate_change() doesn't validate changes in load balance
+ * and spread flags.
+ */
+ if (!balance_flag_changed && !spread_flag_changed) {
+ err = validate_change(cs, trialcs);
+ if (err < 0)
+ goto out;
+ }
+
spin_lock_irq(&callback_lock);
cs->flags = trialcs->flags;
spin_unlock_irq(&callback_lock);
--
2.18.1