On 09/22/2017 07:00 AM, [email protected] wrote: > From: Shu Wang <[email protected]> > > 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 <[email protected]> > --- > 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);
I had actually sent a patch to fix the same bug yesterday. See https://lkml.org/lkml/2017/9/21/333 Cheers, Longman
