How we deal with updates to exclusive cpusets is currently broken. As an example, suppose we have an exclusive cpuset composed of two cpus: A[cpu0,cpu1]. We can assign SCHED_DEADLINE task to it up to the allowed bandwidth. If we want now to modify cpusetA's cpumask, we have to check that removing a cpu's amount of bandwidth doesn't break AC guarantees. This thing isn't checked in the current code.
This patch fixes the problem above, denying an update if the new cpumask won't have enough bandwidth for SCHED_DEADLINE tasks that are currently active. Signed-off-by: Juri Lelli <[email protected]> Reported-by: Peter Zijlstra <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Juri Lelli <[email protected]> Cc: Dario Faggioli <[email protected]> Cc: Michael Trimarchi <[email protected]> Cc: Fabio Checconi <[email protected]> Cc: Li Zefan <[email protected]> Cc: [email protected] Cc: [email protected] --- include/linux/sched.h | 2 ++ kernel/cpuset.c | 10 ++++++++++ kernel/sched/core.c | 21 +++++++++++++++++++++ 3 files changed, 33 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index f225f20..d4ed0db 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2032,6 +2032,8 @@ static inline void tsk_restore_flags(struct task_struct *task, task->flags |= orig_flags & flags; } +extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, + const struct cpumask *trial); extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed); #ifdef CONFIG_SMP diff --git a/kernel/cpuset.c b/kernel/cpuset.c index ab9be24..9066cc7 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -505,6 +505,16 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) goto out; } + /* + * We can't shrink if we won't have enough room for SCHED_DEADLINE + * tasks. + */ + ret = -EBUSY; + if (is_cpu_exclusive(cur) && + !cpuset_cpumask_can_shrink(cur->cpus_allowed, + trial->cpus_allowed)) + goto out; + ret = 0; out: rcu_read_unlock(); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 07ec9bb..35674eb 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4622,6 +4622,27 @@ void init_idle(struct task_struct *idle, int cpu) #endif } +int cpuset_cpumask_can_shrink(const struct cpumask *cur, + const struct cpumask *trial) +{ + int ret = 1, trial_cpus; + struct dl_bw *cur_dl_b; + unsigned long flags; + + rcu_read_lock_sched(); + cur_dl_b = dl_bw_of(cpumask_any(cur)); + trial_cpus = cpumask_weight(trial); + + raw_spin_lock_irqsave(&cur_dl_b->lock, flags); + if (cur_dl_b->bw != -1 && + cur_dl_b->bw * trial_cpus < cur_dl_b->total_bw) + ret = 0; + raw_spin_unlock_irqrestore(&cur_dl_b->lock, flags); + rcu_read_unlock_sched(); + + return ret; +} + int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed) { -- 2.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
