Re: [PATCH v2 3/3] cgroup/cpuset: Do housekeeping check when isolated child with root parent may get more xcpus

[Guopeng Zhang <guopeng.zhang@linux.dev>]

在 2026/10/31 03:07, Waiman Long 写道:
> It is reported by sashiko and Guopeng that when an isolated child with
> root parent gets more isolated CPUs from the expansion of the parent's
> effective_xcpus, it is possible that all the active housekeeping CPUs
> may be gone. So a prstate_housekeeping_conflict() should be performed
> when that happens. Add the check to make sure that we can't exhaust
> all the active housekeeping CPUs.
> 
> Test cases are added to the NOHZ_FULL_TEST_MATRIX of test_cpuset_prs.sh
> to test that.
> 
> Reported-by: Guopeng Zhang <guopeng.zhang@linux.dev>
> Link: https://lore.kernel.org/lkml/ed6fecb4-38e9-4a73-8c1a-7bdd80175a69@linux.dev
> Fixes: e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2")
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  kernel/cgroup/cpuset.c                         | 18 +++++++++++++++---
>  .../selftests/cgroup/test_cpuset_prs.sh        | 10 ++++++++--
>  2 files changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index ed014ecb770c..6e136888fc8e 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -2119,10 +2119,22 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
>  			 * If there is an expansion of parent's effective_xcpus,
>  			 * we may take more xcpus from parent. The parent's
>  			 * effective_cpus should still have active CPUs or nocpu
> -			 * should have been set.
> +			 * should have been set. We also need to do a
> +			 * housekeeping check for an isolated child with root
> +			 * parent to make sure that it won't exhaust all the
> +			 * active housekeeping CPUs.
>  			 */
> -			deleting = cpumask_andnot(tmp->delmask, tmp->delmask,
> -						  cs->effective_xcpus);
> +			cpumask_andnot(tmp->addmask, cs->effective_xcpus, tmp->delmask);
> +			if ((parent_prs == PRS_ROOT) && (old_prs == PRS_ISOLATED) &&
> +			    prstate_housekeeping_conflict(old_prs, parent_prs,
> +							  tmp->delmask, tmp->addmask)) {
> +				adding = cpumask_and(tmp->addmask, cs->effective_xcpus,
> +						     tmp->delmask);
> +				part_error = PERR_HKEEPING;
> +			} else {
> +				deleting = cpumask_andnot(tmp->delmask, tmp->delmask,
> +							  cs->effective_xcpus);
> +			}
>  		} else if (is_partition_invalid(cs)) {
>  			struct cgroup_subsys_state *css;
>  			struct cpuset *child;
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index 844efdf029cd..bdca6c471f87 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -137,7 +137,8 @@ LAST_PRESENT_CPU=$(cat /sys/devices/system/cpu/present | sed -e "s/.*[,-]//")
>  # If isolated CPUs have been reserved at boot time (as shown in
>  # /sys/devices/system/cpu/isolated), these isolated CPUs should be outside of
>  # CPUs 0-8 that will be used by this script for testing purpose. If not, some
> -# of the tests may fail incorrectly.
> +# of the tests may fail incorrectly. The first boot isolated CPU should be
> +# 10 or above.
>  #
>  # The current set of isolated CPUs (as shown in cpuset.cpus.isolated) should
>  # be the same as the boot value. If not, wait a bit and retry again just in
> @@ -156,7 +157,7 @@ TEST_ISOLCPUS=
>  [[ -n "$BOOT_ISOLCPUS" ]] && {
>  	FIRST_ISOLCPUS=$(echo $BOOT_ISOLCPUS | sed -e "s/[,-].*//")
>  	echo "Boot isolated CPUs: $BOOT_ISOLCPUS"
> -	[[ $FIRST_ISOLCPUS -le 8 ]] &&
> +	[[ $FIRST_ISOLCPUS -le 9 ]] &&
>  		skip_test "Boot isolated CPUs overlap CPUs to be tested"
>  }
>  
> @@ -602,6 +603,7 @@ ISOLCPUS_TEST_MATRIX=(
>  )
>  
>  # Test matrix to be run when boot time nohz_full CPUs cover all CPUs except CPUs 0-7
> +# This also means that CPU 8 is available and is a nohz_full CPU.
>  NOHZ_FULL_TEST_MATRIX=(
>  	#  old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
>  	#  ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
> @@ -610,6 +612,10 @@ NOHZ_FULL_TEST_MATRIX=(
>  	" C2-7:P2    .      .      .     C0-4    .      .      .     0 A1:0-4 A1:P2 0-4"
>  	" C1-7:P2 C5-7:P2   .      .       .     .      .    C0:P2   0 A1:1-4|A2:5-7|B1:0
>  								       A1:P2|A2:P2|B1:P-2 1-7"
> +	# An isolated child partition cannot grow to take over the last
> +	# housekeeping CPU when its parent expands the exclusive CPUs.
> +	" C0-8:X1-8:P1 CX0-8:P2 .  .     X0-7    .      .      .     0 A1:0-7|A2:0-7 A1:P1|A2:P-2 ."
> +	" C0-8:X0-6:P1 CX0-8:P2 .  .     X2-8    .      .      .     0 A1:|A2:2-8 A1:P1|A2:P2 2-8"
>  )
>  
>  #

Reviewed-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Tested-by: Guopeng Zhang <zhangguopeng@kylinos.cn>

Thanks,
Guopeng