The current cpuset code uses the global cpuset_attach_old_cs variable
to store the old cpuset value between consecutive cpuset_can_attach()
and cpuset_attach() calls. Since a caller of cpuset_can_attach() may
not need to hold the global cgroup_threadgroup_rwsem, parallel cpuset
attach operations are possible.
When there are concurrent cpuset attach operations in progress,
cpuset_attach() may fetch the wrong value from cpuset_attach_old_cs
causing incorrect result. To avoid this problem while still allowing
certain level of parallelism, drop cpuset_attach_old_cs and use a
per-cpuset attach_old_cs value. Also restrict to at most one active
attach operation per cpuset to avoid corrupting the value of the
per-cpuset attach_old_cs value.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 2367de611c42..3f925c261513 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -198,6 +198,8 @@ struct cpuset {
/* Handle for cpuset.cpus.partition */
struct cgroup_file partition_file;
+
+ struct cpuset *attach_old_cs;
};
/*
@@ -2456,22 +2458,27 @@ static int fmeter_getrate(struct fmeter *fmp)
return val;
}
-static struct cpuset *cpuset_attach_old_cs;
-
/* Called by cgroups to determine if a cpuset is usable; cpuset_rwsem held */
static int cpuset_can_attach(struct cgroup_taskset *tset)
{
struct cgroup_subsys_state *css;
- struct cpuset *cs;
+ struct cpuset *cs, *oldcs;
struct task_struct *task;
int ret;
/* used later by cpuset_attach() */
- cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
+ oldcs = task_cs(cgroup_taskset_first(tset, &css));
cs = css_cs(css);
percpu_down_write(&cpuset_rwsem);
+ /*
+ * Only one cpuset attach operation is allowed for each cpuset.
+ */
+ ret = -EBUSY;
+ if (cs->attach_in_progress)
+ goto out_unlock;
+
/* allow moving tasks into an empty cpuset if on default hierarchy */
ret = -ENOSPC;
if (!is_in_v2_mode() &&
@@ -2498,6 +2505,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
* changes which zero cpus/mems_allowed.
*/
cs->attach_in_progress++;
+ cs->attach_old_cs = oldcs;
ret = 0;
out_unlock:
percpu_up_write(&cpuset_rwsem);
@@ -2548,7 +2556,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
struct task_struct *leader;
struct cgroup_subsys_state *css;
struct cpuset *cs;
- struct cpuset *oldcs = cpuset_attach_old_cs;
+ struct cpuset *oldcs;
bool cpus_updated, mems_updated;
cgroup_taskset_first(tset, &css);
@@ -2556,6 +2564,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
lockdep_assert_cpus_held(); /* see cgroup_attach_lock() */
percpu_down_write(&cpuset_rwsem);
+ oldcs = cs->attach_old_cs;
cpus_updated = !cpumask_equal(cs->effective_cpus,
oldcs->effective_cpus);
mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems);
--
2.31.1
