kernel.git/kernel/cgroup/cpuset.c, branch linux-rolling-lts

cgroup/cpuset: Fix incorrect use of cpuset_update_tasks_cpumask() in update_cpumasks_hier()

2026-03-12T11:09:14Z

[ Upstream commit 68230aac8b9aad243626fbaf3ca170012c17fec5 ] Commit e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2") incorrectly changed the 2nd parameter of cpuset_update_tasks_cpumask() from tmp->new_cpus to cp->effective_cpus. This second parameter is just a temporary cpumask for internal use. The cpuset_update_tasks_cpumask() function was originally called update_tasks_cpumask() before commit 381b53c3b549 ("cgroup/cpuset: rename functions shared between v1 and v2"). This mistake can incorrectly change the effective_cpus of the cpuset when it is the top_cpuset or in arm64 architecture where task_cpu_possible_mask() may differ from cpu_possible_mask. So far top_cpuset hasn't been passed to update_cpumasks_hier() yet, but arm64 arch can still be impacted. Fix it by reverting the incorrect change. Fixes: e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2") Signed-off-by: Waiman Long Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin

mm/vmscan: fix demotion targets checks in reclaim/demotion

2026-03-04T12:21:29Z

[ Upstream commit 1aceed565ff172fc0331dd1d5e7e65139b711139 ] Patch series "mm/vmscan: fix demotion targets checks in reclaim/demotion", v9. This patch series addresses two issues in demote_folio_list(), can_demote(), and next_demotion_node() in reclaim/demotion. 1. demote_folio_list() and can_demote() do not correctly check demotion target against cpuset.mems_effective, which will cause (a) pages to be demoted to not-allowed nodes and (b) pages fail demotion even if the system still has allowed demotion nodes. Patch 1 fixes this bug by updating cpuset_node_allowed() and mem_cgroup_node_allowed() to return effective_mems, allowing directly logic-and operation against demotion targets. 2. next_demotion_node() returns a preferred demotion target, but it does not check the node against allowed nodes. Patch 2 ensures that next_demotion_node() filters against the allowed node mask and selects the closest demotion target to the source node. This patch (of 2): Fix two bugs in demote_folio_list() and can_demote() due to incorrect demotion target checks against cpuset.mems_effective in reclaim/demotion. Commit 7d709f49babc ("vmscan,cgroup: apply mems_effective to reclaim") introduces the cpuset.mems_effective check and applies it to can_demote(). However: 1. It does not apply this check in demote_folio_list(), which leads to situations where pages are demoted to nodes that are explicitly excluded from the task's cpuset.mems. 2. It checks only the nodes in the immediate next demotion hierarchy and does not check all allowed demotion targets in can_demote(). This can cause pages to never be demoted if the nodes in the next demotion hierarchy are not set in mems_effective. These bugs break resource isolation provided by cpuset.mems. This is visible from userspace because pages can either fail to be demoted entirely or are demoted to nodes that are not allowed in multi-tier memory systems. To address these bugs, update cpuset_node_allowed() and mem_cgroup_node_allowed() to return effective_mems, allowing directly logic-and operation against demotion targets. Also update can_demote() and demote_folio_list() accordingly. Bug 1 reproduction: Assume a system with 4 nodes, where nodes 0-1 are top-tier and nodes 2-3 are far-tier memory. All nodes have equal capacity. Test script: echo 1 > /sys/kernel/mm/numa/demotion_enabled mkdir /sys/fs/cgroup/test echo +cpuset > /sys/fs/cgroup/cgroup.subtree_control echo "0-2" > /sys/fs/cgroup/test/cpuset.mems echo $$ > /sys/fs/cgroup/test/cgroup.procs swapoff -a # Expectation: Should respect node 0-2 limit. # Observation: Node 3 shows significant allocation (MemFree drops) stress-ng --oomable --vm 1 --vm-bytes 150% --mbind 0,1 Bug 2 reproduction: Assume a system with 6 nodes, where nodes 0-2 are top-tier, node 3 is a far-tier node, and nodes 4-5 are the farthest-tier nodes. All nodes have equal capacity. Test script: echo 1 > /sys/kernel/mm/numa/demotion_enabled mkdir /sys/fs/cgroup/test echo +cpuset > /sys/fs/cgroup/cgroup.subtree_control echo "0-2,4-5" > /sys/fs/cgroup/test/cpuset.mems echo $$ > /sys/fs/cgroup/test/cgroup.procs swapoff -a # Expectation: Pages are demoted to Nodes 4-5 # Observation: No pages are demoted before oom. stress-ng --oomable --vm 1 --vm-bytes 150% --mbind 0,1,2 Link: https://lkml.kernel.org/r/20260114205305.2869796-1-bingjiao@google.com Link: https://lkml.kernel.org/r/20260114205305.2869796-2-bingjiao@google.com Fixes: 7d709f49babc ("vmscan,cgroup: apply mems_effective to reclaim") Signed-off-by: Bing Jiao Acked-by: Shakeel Butt Cc: Axel Rasmussen Cc: David Hildenbrand Cc: Gregory Price Cc: Johannes Weiner Cc: Joshua Hahn Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Muchun Song Cc: Qi Zheng Cc: Roman Gushchin Cc: Suren Baghdasaryan Cc: Tejun Heo Cc: Vlastimil Babka Cc: Waiman Long Cc: Wei Xu Cc: Yuanchu Xie Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin

cgroup/cpuset: Don't fail cpuset.cpus change in v2

2026-03-04T12:19:56Z

[ Upstream commit 6e6f13f6d5095f3a432da421e78f4d7d51ef39c8 ] Commit fe8cd2736e75 ("cgroup/cpuset: Delay setting of CS_CPU_EXCLUSIVE until valid partition") introduced a new check to disallow the setting of a new cpuset.cpus.exclusive value that is a superset of a sibling's cpuset.cpus value so that there will at least be one CPU left in the sibling in case the cpuset becomes a valid partition root. This new check does have the side effect of failing a cpuset.cpus change that make it a subset of a sibling's cpuset.cpus.exclusive value. With v2, users are supposed to be allowed to set whatever value they want in cpuset.cpus without failure. To maintain this rule, the check is now restricted to only when cpuset.cpus.exclusive is being changed not when cpuset.cpus is changed. The cgroup-v2.rst doc file is also updated to reflect this change. Signed-off-by: Waiman Long Reviewed-by: Chen Ridong Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin

cpuset: Fix missing adaptation for cpuset_is_populated

2026-02-19T15:31:35Z

Commit b1bcaed1e39a ("cpuset: Treat cpusets in attaching as populated") was backported to the long‑term support (LTS) branches. However, because commit d5cf4d34a333 ("cgroup/cpuset: Don't track # of local child partitions") was not backported, a corresponding adaptation to the backported code is still required. To ensure correct behavior, replace cgroup_is_populated with cpuset_is_populated in the partition_is_populated function. Cc: stable@vger.kernel.org # 6.1+ Fixes: b1bcaed1e39a ("cpuset: Treat cpusets in attaching as populated") Cc: Waiman Long Cc: Tejun Heo Signed-off-by: Chen Ridong Signed-off-by: Greg Kroah-Hartman

cpuset: fix warning when disabling remote partition

2026-01-08T09:16:43Z

[ Upstream commit aa7d3a56a20f07978d9f401e13637a6479b13bd0 ] A warning was triggered as follows: WARNING: kernel/cgroup/cpuset.c:1651 at remote_partition_disable+0xf7/0x110 RIP: 0010:remote_partition_disable+0xf7/0x110 RSP: 0018:ffffc90001947d88 EFLAGS: 00000206 RAX: 0000000000007fff RBX: ffff888103b6e000 RCX: 0000000000006f40 RDX: 0000000000006f00 RSI: ffffc90001947da8 RDI: ffff888103b6e000 RBP: ffff888103b6e000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000001 R11: ffff88810b2e2728 R12: ffffc90001947da8 R13: 0000000000000000 R14: ffffc90001947da8 R15: ffff8881081f1c00 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f55c8bbe0b2 CR3: 000000010b14c000 CR4: 00000000000006f0 Call Trace: update_prstate+0x2d3/0x580 cpuset_partition_write+0x94/0xf0 kernfs_fop_write_iter+0x147/0x200 vfs_write+0x35d/0x500 ksys_write+0x66/0xe0 do_syscall_64+0x6b/0x390 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f55c8cd4887 Reproduction steps (on a 16-CPU machine): # cd /sys/fs/cgroup/ # mkdir A1 # echo +cpuset > A1/cgroup.subtree_control # echo "0-14" > A1/cpuset.cpus.exclusive # mkdir A1/A2 # echo "0-14" > A1/A2/cpuset.cpus.exclusive # echo "root" > A1/A2/cpuset.cpus.partition # echo 0 > /sys/devices/system/cpu/cpu15/online # echo member > A1/A2/cpuset.cpus.partition When CPU 15 is offlined, subpartitions_cpus gets cleared because no CPUs remain available for the top_cpuset, forcing partitions to share CPUs with the top_cpuset. In this scenario, disabling the remote partition triggers a warning stating that effective_xcpus is not a subset of subpartitions_cpus. Partitions should be invalidated in this case to inform users that the partition is now invalid(cpus are shared with top_cpuset). To fix this issue: 1. Only emit the warning only if subpartitions_cpus is not empty and the effective_xcpus is not a subset of subpartitions_cpus. 2. During the CPU hotplug process, invalidate partitions if subpartitions_cpus is empty. Fixes: f62a5d39368e ("cgroup/cpuset: Remove remote_partition_check() & make update_cpumasks_hier() handle remote partition") Signed-off-by: Chen Ridong Reviewed-by: Waiman Long Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin

cpuset: Treat cpusets in attaching as populated

2025-12-18T13:03:09Z

[ Upstream commit b1bcaed1e39a9e0dfbe324a15d2ca4253deda316 ] Currently, the check for whether a partition is populated does not account for tasks in the cpuset of attaching. This is a corner case that can leave a task stuck in a partition with no effective CPUs. The race condition occurs as follows: cpu0 cpu1 //cpuset A with cpu N migrate task p to A cpuset_can_attach // with effective cpus // check ok // cpuset_mutex is not held // clear cpuset.cpus.exclusive // making effective cpus empty update_exclusive_cpumask // tasks_nocpu_error check ok // empty effective cpus, partition valid cpuset_attach ... // task p stays in A, with non-effective cpus. To fix this issue, this patch introduces cs_is_populated, which considers tasks in the attaching cpuset. This new helper is used in validate_change and partition_is_populated. Fixes: e2d59900d936 ("cgroup/cpuset: Allow no-task partition to have empty cpuset.cpus.effective") Signed-off-by: Chen Ridong Reviewed-by: Waiman Long Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin

cpuset: remove is_prs_invalid helper

2025-09-22T22:57:46Z

The is_prs_invalid helper function is redundant as it serves a similar purpose to is_partition_invalid. It can be fully replaced by the existing is_partition_invalid function, so this patch removes the is_prs_invalid helper. Signed-off-by: Chen Ridong Acked-by: Waiman Long Signed-off-by: Tejun Heo

cpuset: remove impossible warning in update_parent_effective_cpumask

2025-09-22T22:57:46Z

If the parent is not a valid partition, an error will be returned before any partition update command is processed. This means the WARN_ON_ONCE(!is_partition_valid(parent)) can never be triggered, so it is safe to remove. Signed-off-by: Chen Ridong Acked-by: Waiman Long Signed-off-by: Tejun Heo

cpuset: remove redundant special case for null input in node mask update

2025-09-22T22:57:46Z

The nodelist_parse function already handles empty nodemask input appropriately, making it unnecessary to handle this case separately during the node mask update process. Signed-off-by: Chen Ridong Reviewed-by: Waiman Long Signed-off-by: Tejun Heo

cpuset: fix missing error return in update_cpumask

2025-09-19T16:43:27Z

The commit c6366739804f ("cpuset: refactor cpus_allowed_validate_change") inadvertently removed the error return when cpus_allowed_validate_change() fails. This patch restores the proper error handling by returning retval when the validation check fails. Fixes: c6366739804f ("cpuset: refactor cpus_allowed_validate_change") Signed-off-by: Chen Ridong Signed-off-by: Tejun Heo