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cgroup/cpuset: Prevent recursive call of remote_cpus_update() via update_cpumasks_hier()

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Guopeng reports that changing the cpumask of a remote partition root
may set the effective_cpus of the top_cpuset incorrectly. It is
due to the following call sequence:

  update_cpumask()
   -> partition_cpus_change()
    -> remote_cpus_update()
     -> update_sibling_cpumasks()
      -> update_cpumasks_hier()
       -> remote_cpus_update()

The second remote_cpus_update() call passes in the cs->effective_xcpus
instead of the trialcs->effective_xcpus of the first remote_cpus_update()
call.  As a result, the second call can revert what has been done in
the first call leading to incorrect effective_cpus of the top_cpuset
as well as subpartitions_cpus.

Fix that by adding a new remote_partition_updating flag into the cpuset
structure to indicate that a remote partition is being updated and
update_cpumasks_hier() should skip the whole subtree as update_cpumask()
or update_exclusive_cpumask() which calls partition_cpus_change()
will eventually calls update_cpumasks_hier() for that subtree anyway.

This new flag is currently set only in remote_cpus_update() to prevent
recursive call of remote_cpus_update() on the same cpuset.

A test case is added to test_cpuset_prs.sh to verify this change.

Reported-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Link: https://lore.kernel.org/lkml/20261010075947.333549-2-guopeng.zhang@linux.dev
Reviewed-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Tested-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Fixes: f62a5d3936 ("cgroup/cpuset: Remove remote_partition_check() & make update_cpumasks_hier() handle remote partition")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Waiman Long 2026-10-25 17:44:44 -04:00 committed by Tejun Heo
parent 40a0d5c05a
commit 10a6f00d82
3 changed files with 15 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
kernel/cgroup/cpuset-internal.h
View File

@ -161,6 +161,11 @@ struct cpuset {
*/
bool remote_partition;
/*
* Set to true when a remote partition is undergoing update.
*/
bool remote_partition_updating;
/*
* number of SCHED_DEADLINE tasks attached to this cpuset, so that we
* know when to rebuild associated root domain bandwidth information.

13
kernel/cgroup/cpuset.c
View File

@ -1775,6 +1775,7 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
goto invalidate;
}
cs->remote_partition_updating = true;
spin_lock_irq(&callback_lock);
if (adding)
partition_xcpus_add(prs, NULL, tmp->addmask);
@ -1796,6 +1797,7 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
*/
cpuset_update_tasks_cpumask(&top_cpuset, tmp->new_cpus);
update_sibling_cpumasks(&top_cpuset, NULL, tmp);
cs->remote_partition_updating = false;
return;
invalidate:
@ -2237,16 +2239,19 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
old_prs = new_prs = cp->partition_root_state;
/*
* For child remote partition root (!= cs), we need to call
* remote_cpus_update() if effective_xcpus will be changed.
* Otherwise, we can skip the whole subtree.
* For a child remote partition with remote_partition_updating
* set, we can skip the whole subtree as the this function will
* be called eventually. We can also skip the subtree if the
* effective_xcpus isn't going to be changed. Otherwise, we
* will have to call remote_cpus_update().
*
* remote_cpus_update() will reuse tmp->new_cpus only after
* its value is being processed.
*/
if (remote && (cp != cs)) {
compute_excpus(cp, tmp->new_cpus);
if (cpumask_equal(cp->effective_xcpus, tmp->new_cpus)) {
if (cp->remote_partition_updating ||
cpumask_equal(cp->effective_xcpus, tmp->new_cpus)) {
pos_css = css_rightmost_descendant(pos_css);
continue;
}

1
tools/testing/selftests/cgroup/test_cpuset_prs.sh
View File

@ -347,6 +347,7 @@ TEST_MATRIX=(
" C0-3 C1-3 C2-3 C4 X2-3 X2-3 X2-3:P2 P2:C4-5 0 A3:2-3|B1:4-5 A3:P2|B1:P2 2-5"
" C4:X0-3 X1-3 X2-3 . . P2 . . 0 A1:4|A2:1-3|A3:1-3 A2:P2 1-3"
" C4:X0-3 X1-3 X2-3 . . . P2 . 0 A1:4|A2:4|A3:2-3 A3:P2 2-3"
" CX1-6 C1-4:P1 . C4-5 . C1-3 . . 0 A1:4-6|A2:1-3|B1:4-5 A2:P1"
# Nested remote/local partition tests
" C0-3 C1-3 C2-3 C4-5 X2-3 X2-3:P1 P2 P1 0 A1:0-1|A2:|A3:2-3|B1:4-5 \