From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:40388 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726700AbeJKXJc (ORCPT ); Thu, 11 Oct 2018 19:09:32 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Prateek Sood , Tejun Heo , Amit Pundir Subject: [PATCH 4.4 14/27] cgroup: Fix deadlock in cpu hotplug path Date: Thu, 11 Oct 2018 17:35:01 +0200 Message-Id: <20181011152534.702592242@linuxfoundation.org> In-Reply-To: <20181011152534.014964888@linuxfoundation.org> References: <20181011152534.014964888@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Prateek Sood 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 Signed-off-by: Tejun Heo [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 Signed-off-by: Greg Kroah-Hartman --- 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. kernel/cgroup.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4083,7 +4083,11 @@ int cgroup_transfer_tasks(struct cgroup */ 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);