On 2026/4/17 11:37, Guopeng Zhang wrote:
> cpuset_can_attach() allocates DL bandwidth only when migrating
> deadline tasks to a disjoint CPU mask, but cpuset_cancel_attach()
> rolls back based only on nr_migrate_dl_tasks. This makes the DL
> bandwidth alloc/free paths asymmetric: rollback can call dl_bw_free()
> even when no dl_bw_alloc() was done.
>
> Rollback also needs to undo the reservation against the same CPU/root
> domain that was charged. Record the CPU used by dl_bw_alloc() and use
> that state in cpuset_cancel_attach(). If no allocation happened,
> dl_bw_cpu stays at -1 and rollback skips dl_bw_free(). If allocation
> did happen, bandwidth is returned to the same CPU/root domain.
>
> Successful attach paths are unchanged. This only fixes failed attach
> rollback accounting.
>
> Fixes: 2ef269ef1ac0 ("cgroup/cpuset: Free DL BW in case can_attach() fails")
> Signed-off-by: Guopeng Zhang <[email protected]>
> ---
> kernel/cgroup/cpuset-internal.h | 5 +++++
> kernel/cgroup/cpuset.c | 13 +++++++++----
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
> index fd7d19842ded..bb4e692bea30 100644
> --- a/kernel/cgroup/cpuset-internal.h
> +++ b/kernel/cgroup/cpuset-internal.h
> @@ -168,6 +168,11 @@ struct cpuset {
> int nr_deadline_tasks;
> int nr_migrate_dl_tasks;
> u64 sum_migrate_dl_bw;
> + /*
> + * CPU used for temporary DL bandwidth allocation during attach;
> + * -1 if no DL bandwidth was allocated in the current attach.
> + */
> + int dl_bw_cpu;
>
> /* Invalid partition error code, not lock protected */
> enum prs_errcode prs_err;
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 1335e437098e..e3a081a07c6d 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -288,6 +288,7 @@ struct cpuset top_cpuset = {
> .flags = BIT(CS_CPU_EXCLUSIVE) |
> BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),
> .partition_root_state = PRS_ROOT,
> + .dl_bw_cpu = -1,
> };
>
> /**
> @@ -579,6 +580,8 @@ static struct cpuset *dup_or_alloc_cpuset(struct cpuset
> *cs)
> if (!trial)
> return NULL;
>
> + trial->dl_bw_cpu = -1;
> +
> /* Setup cpumask pointer array */
> cpumask_var_t *pmask[4] = {
> &trial->cpus_allowed,
> @@ -2980,6 +2983,7 @@ static void reset_migrate_dl_data(struct cpuset *cs)
> {
> cs->nr_migrate_dl_tasks = 0;
> cs->sum_migrate_dl_bw = 0;
> + cs->dl_bw_cpu = -1;
> }
>
> /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
> @@ -3056,6 +3060,8 @@ static int cpuset_can_attach(struct cgroup_taskset
> *tset)
> reset_migrate_dl_data(cs);
> goto out_unlock;
> }
> +
> + cs->dl_bw_cpu = cpu;
> }
>
> out_success:
> @@ -3080,12 +3086,11 @@ static void cpuset_cancel_attach(struct
> cgroup_taskset *tset)
> mutex_lock(&cpuset_mutex);
> dec_attach_in_progress_locked(cs);
>
> - if (cs->nr_migrate_dl_tasks) {
> - int cpu = cpumask_any(cs->effective_cpus);
> + if (cs->dl_bw_cpu >= 0)
> + dl_bw_free(cs->dl_bw_cpu, cs->sum_migrate_dl_bw);
>
> - dl_bw_free(cpu, cs->sum_migrate_dl_bw);
> + if (cs->nr_migrate_dl_tasks)
> reset_migrate_dl_data(cs);
> - }
>
> mutex_unlock(&cpuset_mutex);
> }
Good catch.
Reviewed-by: Chen Ridong <[email protected]>
--
Best regards,
Ridong
