在 2026/10/14 22:05, Waiman Long 写道:
> Although it is not typical for real users to create a complicated nested
> partition hierarchy, it is currently allowed to create nested root and
> isolated partitions. In addition, disabling or invalidating a partition
> should always be allowed especially when the cpuset is being deleted.
>
> With a nested root and isolated partition hierarchy, it is possible
> that all active housekeeping CPUs can be exhausted when disabling or
> invalidating a root partition and returning its CPUs to the isolated
> parent.
>
> One way to avoid this problem is to disallow the creation of a root
> partition under an isolated parent. It is indeed a new limitation imposed
> on the existing cpuset partition functionality. However an isolated
> partition is usually a left node where scheduling and some other kernel
> noises are disabled. It doesn't make much sense to create a child root
> partition under an isolated parent and remove some CPUs from the set
> of isolated CPUs again. Creation of a child isolated partition under a
> root or isolated parent is still allowed.
>
> The cgroup-v2 documentation is also updated to reflect this new
> limitation. New test cases are added to test_cpuset_prs.sh to verify
> this new behavior. Some existing test cases are also updated accordingly.
>
> Signed-off-by: Waiman Long <[email protected]>
> ---
> Documentation/admin-guide/cgroup-v2.rst | 4 +++-
> kernel/cgroup/cpuset-internal.h | 1 +
> kernel/cgroup/cpuset.c | 13 +++++++++++++
> tools/testing/selftests/cgroup/test_cpuset_prs.sh | 14 ++++++++------
> 4 files changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst
> b/Documentation/admin-guide/cgroup-v2.rst
> index bd8c80f3bbc9..2c445829e24d 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -2767,7 +2767,9 @@ Cpuset Interface Files
> be retained, but behaves more like a "member".
>
> All possible state transitions among "member", "root" and
> - "isolated" are allowed.
> + "isolated" are allowed with the exception that a local child
> + "root" partition is not allowed to be created under an "isolated"
> + parent partition.
>
> On read, the "cpuset.cpus.partition" file can show the following
> values.
> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
> index 5da9c91295b0..2e44dc8634dc 100644
> --- a/kernel/cgroup/cpuset-internal.h
> +++ b/kernel/cgroup/cpuset-internal.h
> @@ -35,6 +35,7 @@ enum prs_errcode {
> PERR_HKEEPING,
> PERR_ACCESS,
> PERR_REMOTE,
> + PERR_ISOPARENT,
> };
>
> /* bits in struct cpuset flags field */
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 40c004386af0..681701ba46e1 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -60,6 +60,7 @@ static const char * const perr_strings[] = {
> [PERR_HKEEPING] = "partition config conflicts with housekeeping setup",
> [PERR_ACCESS] = "Enable partition not permitted",
> [PERR_REMOTE] = "Have remote partition underneath",
> + [PERR_ISOPARENT] = "Root partition is not allowed with isolated parent",
> };
>
> /*
> @@ -2865,6 +2866,7 @@ static int update_prstate(struct cpuset *cs, int
> new_prs)
> int err = PERR_NONE, old_prs = cs->partition_root_state;
> struct cpuset *parent = parent_cs(cs);
> struct tmpmasks tmpmask;
> + int parent_prs = parent->partition_root_state;
> bool isolcpus_updated = false;
> bool disable_partition = false;
>
> @@ -2910,6 +2912,14 @@ static int update_prstate(struct cpuset *cs, int
> new_prs)
> enum partition_cmd cmd = (new_prs == PRS_ROOT)
> ? partcmd_enable :
> partcmd_enablei;
>
> + /*
> + * It is not allowed to create a root partition under
> + * an isolated parent partition.
> + */
> + if ((new_prs == PRS_ROOT) && (parent_prs ==
> PRS_ISOLATED)) {
> + err = PERR_ISOPARENT;
> + goto out;
> + }
I tested the following case. Writing root initially leaves C invalid, but
updating its cpuset.cpus makes it valid again.
CPUs 0-15 are online, with nohz_full=2-15 and no isolcpus:
# cd /sys/fs/cgroup
# echo +cpuset > cgroup.subtree_control
# mkdir A
# echo 1-2 > A/cpuset.cpus
# echo isolated > A/cpuset.cpus.partition
# echo +cpuset > A/cgroup.subtree_control
# mkdir A/C
# echo 1 > A/C/cpuset.cpus
# echo root > A/C/cpuset.cpus.partition
# cat A/C/cpuset.cpus.partition
root invalid (Root partition is not allowed with isolated parent)
# echo 1-2 > A/C/cpuset.cpus
# cat A/C/cpuset.cpus.partition
root
C becomes a valid root partition.
Thanks,
Guopeng
> err = update_parent_effective_cpumask(cs, cmd, NULL,
> &tmpmask);
> } else {
> err = remote_partition_enable(cs, new_prs, &tmpmask);
> @@ -2922,6 +2932,9 @@ static int update_prstate(struct cpuset *cs, int
> new_prs)
> if (prstate_housekeeping_conflict(new_prs,
> cs->effective_xcpus)) {
> disable_partition = true;
> err = PERR_HKEEPING;
> + } else if (parent_prs == PRS_ISOLATED) {
> + disable_partition = true;
> + err = PERR_ISOPARENT;
> } else {
> isolcpus_updated = true;
> }
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index 874a8a161236..85a4f87840b4 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -288,16 +288,12 @@ TEST_MATRIX=(
>
> A1:P0|A2:P1|A3:P0|B1:P1"
> " C0-3 C1-3 C3 C4 X2-3 X2-3:P1 P2 P1 0
> A1:0-1|A2:2|A3:3|B1:4 \
>
> A1:P0|A2:P1|A3:P2|B1:P1 2-4|3"
> - " C0-4 C1-4 C2-4 . X2-4 X2-4:P2 X4:P1 . 0
> A1:0-1|A2:2-3|A3:4 \
> -
> A1:P0|A2:P2|A3:P1 2-4|2-3"
> - " C0-4 C1-4 C2-4 . X2-4 X2-4:P2 X3-4:P1 . 0
> A1:0-1|A2:2|A3:3-4 \
> -
> A1:P0|A2:P2|A3:P1 2"
> " C0-4:X2-4 C1-4:X2-4:P1 C2-4:X4:P2 \
> . . X5 . . 0
> A1:0-4|A2:1-4|A3:2-4 \
>
> A1:P0|A2:P-1|A3:P-2 ."
> - " C0-4:X2-4 C1-4:X2-4:P2 C2-4:X4:P1 \
> + " C0-4:X2-4 C1-4:X2-4:P1 C2-4:X4:P2 \
> . . . X1 . 0
> A1:0-1|A2:2-4|A3:2-4 \
> -
> A1:P0|A2:P2|A3:P-1 2-4"
> +
> A1:P0|A2:P1|A3:P-2 ."
> " CX1-3:P1 CX1-3 CX1-3 . . . P1 . 0
> A1:1-3|A2:1-3|A3:1-3 \
>
> A1:P1|A2:P0|A3:P-1"
>
> @@ -430,6 +426,12 @@ TEST_MATRIX=(
> # cpuset.cpus can become empty with task in it as it inherits parent's
> effective CPUs
> " C1-3 C2 . . . T:C . . 0
> A1:1-3|A2:1-3"
>
> + # Creation of root partition under an isolated partition is not allowed
> + " C1-3:P2 C2 . . . P1 . . 0
> A1:1-3|A2:2 A1:P2|A2:P-1 1-3"
> + " C1-3:P2 C2 . . . P2 . . 0
> A1:1,3|A2:2 A1:P2|A2:P2 1-3"
> + " C1-3:P2 C2:P2 . . . P1 . . 0
> A1:1-3|A2:2 A1:P2|A2:P-1 1-3"
> +
> + #
> # old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs
> Pstate ISOLCPUS
> # ------ ------ ------ ------ ------ ------ ------ ------ ---- -----
> ------ --------
> # Failure cases:
