From: Shu Wang <shuw...@redhat.com>
cgroup_migrate assumes mgctx tset.csets is pointing to
tset.src_csets at start, add tasks to tset.src_csets in
func cgroup_migrate_add_task, change test.csets to
tset.dst_csets in cgroup_migrate_execute.
For offline a cpu in cgroup_transfer_tasks, it will first
migrate a task and cause tset.csets pointing to dst_csets.
Get a NULL pointer in cgroup_taskset_first.
reproducer on my 2 cpus machine:
mkdir /sys/fs/cgroup/cpuset/test
cd /sys/fs/cgroup/cpuset/test
echo 1 > cpuset.cpus
echo 0 > cpuset.mems
sleep 100 & echo $! > tasks
sleep 100 & echo $! > tasks
echo 0 > /sys/bus/cpu/devices/cpu1/online
backtrace:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000cf8
IP: cpuset_can_attach+0x2f/0x140
Call Trace:
? cpuset_attach+0x30f/0x3d0
cgroup_migrate_execute+0x71/0x3c0
cgroup_migrate+0x75/0x80
cgroup_transfer_tasks+0x1b2/0x230
cpuset_hotplug_workfn+0xa7d/0xce0
? finish_task_switch+0x79/0x240
process_one_work+0x149/0x360
worker_thread+0x4d/0x3c0
Signed-off-by: Shu Wang <shuw...@redhat.com>
---
kernel/cgroup/cgroup-v1.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 024085daab1a..165734573b5e 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -129,6 +129,12 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup
*from)
css_task_iter_end(&it);
if (task) {
+ /*
+ * Reset csets to src_cets, as cgroup_migrate assumes
+ * csets is pointing to src_csets.
+ */
+ mgctx.tset.csets = &mgctx.tset.src_csets;
+
ret = cgroup_migrate(task, false, &mgctx);
if (!ret)
trace_cgroup_transfer_tasks(to, task, false);
--
2.13.5
