| Message ID | 1539195816-16015-1-git-send-email-amit.pundir@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [for-4.9.y] cgroup: Fix deadlock in cpu hotplug path | expand |
On Wed, Oct 10, 2018 at 11:53:36PM +0530, Amit Pundir wrote: > From: Prateek Sood <prsood@codeaurora.org> > > commit 116d2f7496c51b2e02e8e4ecdd2bdf5fb9d5a641 upstream. > > Deadlock during cgroup migration from cpu hotplug path when a task T is > being moved from source to destination cgroup. > > kworker/0:0 > cpuset_hotplug_workfn() > cpuset_hotplug_update_tasks() > hotplug_update_tasks_legacy() > remove_tasks_in_empty_cpuset() > cgroup_transfer_tasks() // stuck in iterator loop > cgroup_migrate() > cgroup_migrate_add_task() > > In cgroup_migrate_add_task() it checks for PF_EXITING flag of task T. > Task T will not migrate to destination cgroup. css_task_iter_start() > will keep pointing to task T in loop waiting for task T cg_list node > to be removed. > > Task T > do_exit() > exit_signals() // sets PF_EXITING > exit_task_namespaces() > switch_task_namespaces() > free_nsproxy() > put_mnt_ns() > drop_collected_mounts() > namespace_unlock() > synchronize_rcu() > _synchronize_rcu_expedited() > schedule_work() // on cpu0 low priority worker pool > wait_event() // waiting for work item to execute > > Task T inserted a work item in the worklist of cpu0 low priority > worker pool. It is waiting for expedited grace period work item > to execute. This work item will only be executed once kworker/0:0 > complete execution of cpuset_hotplug_workfn(). > > kworker/0:0 ==> Task T ==>kworker/0:0 > > In case of PF_EXITING task being migrated from source to destination > cgroup, migrate next available task in source cgroup. > > Signed-off-by: Prateek Sood <prsood@codeaurora.org> > Signed-off-by: Tejun Heo <tj@kernel.org> > [AmitP: Upstream commit cherry-pick failed, so I picked the > backported changes from CAF/msm-4.9 tree instead: > https://source.codeaurora.org/quic/la/kernel/msm-4.9/commit/?id=49b74f1696417b270c89cd893ca9f37088928078] > Signed-off-by: Amit Pundir <amit.pundir@linaro.org> > --- > This patch can be cleanly applied and build tested on 4.4.y and 3.18.y > as well but I couldn't find it in msm-4.4 and msm-3.18 trees. So this > patch is really untested on those stable trees. > Build tested on 4.9.131, 4.4.159 and 3.18.123 for ARCH=arm/arm64 allmodconfig. Now applied, thanks. greg k-h
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 4c233437ee1a..bb0cf1caf1cd 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4386,7 +4386,11 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from) */ do { css_task_iter_start(&from->self, &it); - task = css_task_iter_next(&it); + + do { + task = css_task_iter_next(&it); + } while (task && (task->flags & PF_EXITING)); + if (task) get_task_struct(task); css_task_iter_end(&it);