[PATCH 6/7] cgroup/cpuset: Protect DL BW data against parallel cpuset_attach()

[Waiman Long <longman@redhat.com>]

It is possible to have parallel attach operations to the same cpuset in
progress. To avoid possible corruption of single set of DL BW data in
the cpuset structure, we have to disallow parallel attach operations if
DL tasks are present. Attach operations can still proceed in parallel
as long as no DL tasks are involved.

This patch also stores the CPU where DL BW is allocated and free that BW
back to the same CPU in case cpuset_can_attach() is called.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 05c0a1255218..555a6b1a2b76 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -199,6 +199,7 @@ struct cpuset {
 	 */
 	int nr_deadline_tasks;
 	int nr_migrate_dl_tasks;
+	int dl_bw_cpu;
 	u64 sum_migrate_dl_bw;
 
 	/* Invalid partition error code, not lock protected */
@@ -2502,6 +2503,16 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 	if (cpumask_empty(cs->effective_cpus))
 		goto out_unlock;
 
+	/*
+	 * If there is another parallel attach operations in progress for
+	 * the same cpuset, the single set of DL data there may get
+	 * incorrectly overwritten. So parallel operations are not allowed
+	 * if DL tasks are present.
+	 */
+	ret = -EBUSY;
+	if (cs->nr_migrate_dl_tasks)
+		goto out_unlock;
+
 	cgroup_taskset_for_each(task, css, tset) {
 		ret = task_can_attach(task);
 		if (ret)
@@ -2511,6 +2522,9 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 			goto out_unlock;
 
 		if (dl_task(task)) {
+			if (cs->attach_in_progress)
+				goto out_unlock;
+
 			cs->nr_migrate_dl_tasks++;
 			cs->sum_migrate_dl_bw += task->dl.dl_bw;
 		}
@@ -2533,6 +2547,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
 			reset_migrate_dl_data(cs);
 			goto out_unlock;
 		}
+		cs->dl_bw_cpu = cpu;
 	}
 
 out_succes:
@@ -2559,9 +2574,7 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 	cs->attach_in_progress--;
 
 	if (cs->nr_migrate_dl_tasks) {
-		int cpu = cpumask_any(cs->effective_cpus);
-
-		dl_bw_free(cpu, cs->sum_migrate_dl_bw);
+		dl_bw_free(cs->dl_bw_cpu, cs->sum_migrate_dl_bw);
 		reset_migrate_dl_data(cs);
 	}
 
-- 
2.31.1